I 


Report  of  Committee  on  Concrete 
and  Reinforced  Concrete. 


Authorized  Reprint  from  the  Copyrighted 

PROCEEDINGS  OF  THE  AMERICAN  SOCIETY  FOB  TESTING  MATERIALS, 

PHILADELPHIA,  PENNA. 

Volume  XIII,  1913. 


Report  of  Committee  on  Concrete 
and  Reinforced  Concrete. 


Authorized  Reprint  from  the  Copyrighted 

PROCEEDINGS  OP  THE  AMERICAN  SOCIETY  FOR  TESTING  MATERIALS, 

PHILADELPHIA,  PENNA. 

Volume  XIII,   1913. 


v«» 


APPENDIX. 

REPORT  ON  CONCRETE  AND  REINFORCED 
CONCRETE. 

REVISED    AT   THE    MEETING    OF    THE    JOINT    COMMITTEE    ON 

CONCRETE  AND  REINFORCED  CONCRETE,  NEW  YORK,  N.  Y., 

NOVEMBER  20,  1912. 


DECEMBER  1,  1912. 


I.     INTRODUCTION. 

I.     APPOINTMENT  AND  WORK  OF  COMMITTEE. 

In  1903  and  1904  special  committees  were  appointed  by 
the  American  Society  of  Civil  Engineers,  American  Society  for 
Testing  Materials,  American  Railway  Engineering  and  Mainte- 
nance of  Way  Association  and  the  Association  of  American  Port- 
land Cement  Manufacturers,  for  the  purpose  of  investigating 
current  practice  and  providing  definite  information  concerning 
the  properties  of  concrete  and  reinforced  concrete  and  to  recom- 
mend necessary  factors  and  formulas  required  in  the  design  of 
structures  in  which  these  materials  are  used.  The  history  of  the 
appointment  of  the  committees  is  as  follows: 

At  the  annual  convention  of  the  American  Society  of  Civil 
Engineers  held  at  Asheville,  N.  C.,  June  11,  1903,  the  following 
resolution  was  adopted : 

It  is  the  sense  of  this  meeting  that  a  special  committee  be  appointed 
to  take  up  the  question  of  concrete  and  steel  concrete,  and  that  such  com- 
mittee cooperate  with  the  American  Society  for  Testing  Materials  and  the 
American  Railway  Engineering  and  Maintenance  of  Way  Association. 

Following  the  adoption  of  this  resolution,  a  Special  Com- 
mittee on  Concrete  and  Steel  Concrete  was  appointed  by  the 
Board  of  Direction  on  May  31,  1904.  At  the  Annual  Meeting, 
held  January  18,  1905,  the  title  of  this  special  committee  was,  at 

(224) 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     225 

the  request  of  the  Committee,  changed  to  "Special  Committee  on 
Concrete  and  Reinforced  Concrete."  This  Special  Committee 
held  its  first  meeting  at  Atlantic  City,  N.  J.,  June  17,  1904,  and 
effected  an  organization;  Mr.  C.  C.  Schneider  was  appointed 
Chairman  and  Mr.  J.  W.  Schaub,  Secretary.  Mr.  Schneider 
resigned  from  the  Committee  on  January  3,  1911,  and  the  Board 
of  Direction  on  January  31,  1911,  appointed  Mr.  J.  R.  Worcester 
as  Chairman.  On  the  resignation  of  Mr.  J.  W.  Schaub,  Mr. 
Richard  L.  Humphrey  was  appointed  Secretary  on  October  11, 
1905. 

At  the  first  meeting  of  the  Committee  it  was  decided  to 
cooperate  with  similar  committees  which  had  been  appointed 
by  the  American  Society  for  Testing  Materials  and  the  American 
Railway  Engineering  and  Maintenance  of  Way  Association  through 
the  organization  of  a  Joint  Committee  on  Concrete  and  Reinforced 
Concrete. 

At  the  annual  meeting  of  the  American  Society  for  Testing 
Materials  held  July  1,  1903,  at  the  Delaware  Water  Gap,  the 
following  resolution  was  unanimously  adopted: 

That  the  Executive  Committee  be  requested  to  consider  the  desira- 
bility of  appointing  a  committee  on  "Reinforced  Concrete,"  with  a  view  of 
cooperating  with  the  committees  of  other  societies  in  the  study  of  the  subject. 

At  the  meeting  of  the  Executive  Committee  of  the  American 
Society  for  Testing  Materials,  held  December  5,  1903,  a  special 
committee  on  " Reinforced  Concrete"  was  appointed. 

The  American  Railway  Engineering  and  Maintenance  of 
Way  Association  appointed  a  Committee  on  Masonry  on  July 
20,  1899,  with  instructions  as  a  -part  of  its  duties  to  prepare  speci- 
fications for  concrete  masonry.  A  preliminary  set  of  specifications 
for  Portland  cement  concrete  was  reported  to  and  adopted  by 
the  Association  on  March  19,  1903.  At  the  meeting  held  in 
Chicago  on  March  17,  1904,  the  Committee  on  Masonry  was  au- 
thorized to  cooperate  with  the  Special  Committee  on  Concrete 
and  Reinforced  Concrete  of  the  American  Society  of  Civil  En- 
gineers, and  following  this  action  a  special  sub-committee  was 
appointed. 

At  a  meeting  of  the  several  special  committees  representing 
the  above  mentioned  societies,  held  at  Atlantic  City,  N.  J., 
June  17,  1904,  arrangements  were  completed  for  collaborating  the 


226  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

work  of  these  several  committees  through  the  formation  of  the 
Joint  Committee  on  Concrete  and  Reinforced  Concrete.  Mr. 
C.  C.  Schneider  was  elected  temporary  chairman  and  Prof.  A.  N. 
Talbot,  temporary  secretary.  The  proposed  plan  of  action  of 
the  special  committee  of  the  American  Society  of  Civil  Engineers 
was  outlined,  involving  the  appointment  of  sub-committees  on 
Plan  and  Scope,  on  Tests,  and  on  Ways  and  Means. 

The  Joint  Committee,  at  its  first  meeting,  invited  the  Asso- 
ciation of  American  Portland  Cement  Manufacturers  to  join 
in  its  deliberations  through  a  committee  appointed  for  the  pur- 
pose. 

The  Joint  Committee  at  meetings  at  St.  Louis  in  October, 
1904,  and  at  New  York  in  the  following  January  perfected  its 
organization  by  the  adoption  of  rules  and  the  choice  of  Mr.  C.  C. 
Schneider  as  Chairman,  Mr.  Emil  Swensson,  Vice-Chairman, 
and  Mr.  J.  W.  Schaub,  Secretary.  Later,  on  the  resignation  of 
Mr.  Schaub,  Mr.  Richard  L.  Humphrey  was  chosen  Secretary. 
Sub-Committees  on  Plan  and  Scope,  on  Tests,  and  on  Ways  and 
Means,  were  appointed. 

The  Joint  Committee  as  thus  organized,  consisted  of  the 
following  members: 

OFFICERS. 

Chairman — C.  C.  SCHNEIDER. 
Vice-Chairman — EMIL  SWENSSON. 
Secretary — RICHARD  L.  HUMPHREY. 

MEMBERS. 

American  Society  of  Civil  Engineers  (Special  Committee  on  Concrete  and 
Reinforced  Concrete)  : 

Greiner,  J.  E.,  Consulting  Engineer,  Baltimore  and  Ohio  Railroad? 
Baltimore,  Md. 

Hatt,  W.  K.,  Professor  of  Civil  Engineering,  Purdue  University,  Lafay- 
ette, Ind. 

Hoff,  Olaf,  Vice-President,  Butler  Brothers,  Hoff  and  Company,  New 
York,  N.  Y. 

Humphrey,  Richard  L.,  Consulting  Engineer;  Engineer  in  Charge, 
Structural  Materials  Testing  Laboratories,  U.  S.  Geological  Sur- 
vey, Philadelphia,  Pa. 

Lesley,  R.  W.,  President,  American  Cement  Company,  Philadelphia, 
Pa. 

Schaub,  J.  W.,  Consulting  Engineer,  Chicago,  111. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     227 

Schneider,  C.  C.,  Consulting  Engineer,  Philadelphia,  Pa. 

Swensson,  Emil,  Consulting  Engineer,  Pittsburgh,  Pa. 

Talbot,  A.  N.,  Professor  of  Municipal  and  Sanitary  Engineering,  in 

charge  of  Theoretical  and  Applied  Mechanics,  University  of  Illinois, 

Urbana,  111. 
Worcester,  J.  R.,  Consulting  Engineer,  Boston,  Mass. 

American  Society  for  Testing  Materials  (Committee  on  Reinforced  Con- 
crete) : 

Fuller,  William  B.,  Consulting  Engineer,  New  York,  N.  Y. 
Heidenreich,  E.  Lee,  Consulting  Engineer,  New  York,  N.  Y. 
Humphrey,   Richard  L.,   Consulting  Engineer;    Engineer  in   Charge, 

Structural  Materials  Testing  Laboratories,  U.  S.  Geological  Sur- 
vey, Philadelphia,  Pa. 

Johnson,  Albert  L.,  Consulting  Engineer,  St.  Louis,  Mo. 
Lanza,    Gaetano,    Professor   of   Theoretical   and   Applied    Mechanics, 

Massachusetts  Institute  of  Technology,  Boston,  Mass. 
Lssley,  R.  W.,  President,  American  Cement  Company,  Philadelphia, 

Pa. 
Marburg,  Edgar,  Professor  of  Civil  Engineering,  University  of  Penn- 

.sylvania,  Philadelphia.  Pa. 
Mills,  Charles  M.,  Principal  Assistant  Engineer,  Philadelphia  Rapid 

Transit  Company,  Philadelphia,  Pa. 
Moisseiff,  Leon  S.,  Engineer  of  Design,  Department  of  Bridges,  New 

York,  N.  Y. 
Quimby,  Henry  H.,  Assistant,  Engineer  of  Bridges,  Bureau  of  Surveys, 

Philadelphia,  Pa. 
Taylor,  W.  P.,  Engineer  in  Charge  of  Testing  Laboratory,  Philadelphia, 

Pa. 
Thompson,    Sanford    E.,    Consulting    Engineer,    Newton    Highlands, 

Mass. 
Turneaure,  F.  E.,   Dean  of  College  of  Mechanics  and  Engineering, 

University  of  Wisconsin,  Madison,  Wis. 
Wagner,  Samuel  Tobias,  Assistant  Engineer,  Philadelphia  and  Reading 

Railroad,  Philadelphia,  Pa. 
Webster,  George  S.,  Chief  Engineer,  Bureau  of  Surveys,  Philadelphia, 

Pa. 

American  Railway  Engineering  Association  (Sub-Committee  on  Reinforced 
Concrete) : 

Beckwith,  Frank,  Engineer  of  Bridges  and  Structures,  Lake  Shore 
and  Michigan  Southern  Railroad,  Cleveland,  Ohio. 

Boynton,  C.  W.,  Inspecting  Engineer,  Cement  Department,  Illinois 
Steel  Company,  Chicago,  111. 

Cunningham,  A.  O.,  Chief  Engineer,  Wabash  Railroad,  St.  Louis,  Mo. 

Scribner,  Gilbert  H.,  Jr.,  Contracting  Engineer,  Chicago,  111. 

Swain,  George  F.,  Professor  of  Civil  Engineering,  Massachusetts  Insti- 
tute of  Technology,  Boston,  Mass. 


228  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

Association  of  American  Portland  Cement  Manufacturers  (Committee  on 
Concrete  and  Steel  Concrete) : 

Fraser,  Norman  D.,  President,  Chicago  Portland  Cement  Company, 
Chicago,  111. 

Griffiths,  R.  E.,  Vice-President,  American  Cement  Company,  Phila- 
delphia, Pa. 

Hagar,  Edward  M.,  Manager,  Cement  Department,  Illinois  Steel 
Company,  Chicago,  111. 

Newberry,  Spencer  B.,  Manager,  Sandusky  Portland  Cement  Company, 
Sandusky,  Ohio. 

Since  organization  the  following  changes  have  occurred  in 
the  personnel  of  the  Joint  Committee: 

J.  W.  Schaub,  died  March  30,  1909. 

C  C.  Schneider,  resigned  January  3,  1911. 

Ernest  R.  Ackerman,  resigned. 

T.  J.  Brady,  resigned. 

Frank  Beckwith,  resigned. 

A.  O.  Cunningham,  resigned. 

George  F.  Swain,  resigned. 

The    following    representatives    of    the    American    Railway 
Engineering  Association  have  since  been  appointed : 

Thompson,  F.  L.,  Engineer  of  Bridges  and  Buildings,  Illinois  Central 

Railroad,  Chicago,  111. 
Alternates: 

Hotchkiss,  L.  J.,  Assistant  Bridge  Engineer,  Chicago,  Burlington  and 
Quincy  Railroad,  Chicago,  111. 

Prior,  J.  H.,  Assistant  Engineer,  Chicago,  Milwaukee  and  St.  Paul 
Railway,  Chicago,  111. 

Schall,  F.  E.,  Bridge  Engineer,  Lehigh  Valley  Railroad,  South  Beth- 
lehem, Pa. 

Tuthill,  Job,  Assistant  Engineer.  Cincinnati,  Hamilton  and  Dayton 
Railway,  Cincinnati,  Ohio. 

At  a  meeting  of  the  Joint  Committee  held  at  Atlantic  City, 

N.  J.,  June  30,  1911,  Mr.  J.  R.  Worcester  was  elected  chairman. 

Meetings  of  the  Joint  Committee  have  been  held  as  follows: 

June  17,  1904,  at  Atlantic  City,  N.  J. 
Oct.  4,  5,  6,  1904,  at  St.  Louis,  Mo. 
Jan.  17,  1905,  at  New  York,  N.  Y. 
June  21,  1905,  at  Cleveland,  Ohio. 
June  30;  1905,  at  Atlantic  City,  N.  J. 
Oct.  11,  1905,  at  New  York,  N.  Y. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.  229 

Dec.  14,  1905,  at  New  York,  N.  Y. 
June  21,  1906,  at  Atlantic  City,  N.  J. 
Dec.  13,  1906,  at  New  York,  N.  Y. 
Jan.  15,  1907,  at  New  York,  N.  Y. 
March  7,  1907,  at  New  York,  N.  Y. 
March  18,  1907  at  Chicago,  111. 
June  21,  22,  1907,  at  Atlantic  City,  N.  J. 
Dec.  10,  1907,  at  New  York,  N.  Y. 
Oct.  27,  28,  1908,  at  New  York,  N.  Y. 
Dec.  9,  10,  11,  1908,  at  Philadelphia,  Pa. 
June  30,  1911,  at  Atlantic  City,  N.  J. 
Nov.  20,  1912,  at  New  York,  N.  Y. 

At  the  meeting  of  the  Joint  Committee  at  St.  Louis  in  Octo- 
ber, 1904,  it  was  determined  to  arrange  tests  at  such  technologi- 
cal institutions  as  were  provided  with  the  requisite  facilities  and 
were  willing  to  cooperate,  the  Committee,  through  its  Sub-Com- 
mittee on  Ways  and  Means,  to  provide  materials,  and  through  its 
Sub-Committee  on  Tests,  to  consult  as  to  lines  of  testing  and  to 
advise  as  to  methods.  The  following  ten  institutions,  Case 
School  of  Applied  Science,  Columbia  University,  Cornell  Uni- 
versity, University  of  Illinois,  State  University  of  Iowa,  Massa- 
chusetts Institute  of  Technology,  University  of  Minnesota,  Ohio 
State  University,  Purdue  University  and  University  of  Wiscon- 
sin, undertook  a  preliminary  series  of  tests  and  carried  them 
through,  in  due  time  reporting  their  results  to  the  Committee. 

Through  the  inability  of  the  Committee  to  do  as  much  as 
it  had  hoped  by  way  of  furnishing*  uniform  materials  for  these 
tests  and  exercising  a  proper  supervision,  the  results  were  not  as 
serviceable  to  the  Committee  as  they  would  have  been  if  the 
full  plans  had  been  carefully  carried  out;  but  much  important 
information  was  received  in  this  manner,  and  the  Committee 
desires  to  express  its  gratitude  to  the  professors  and  students 
who  so  kindly  assisted  in  this  work. 

The  results  were  collated  and  edited  by  the  Secretary  of  the 
Committee  at  the  Structural  Materials  Testing  Laboratories 
of  the  U.  S.  Geological  Survey,  St.  Louis,  and  the  results  in  type- 
written form  were  circulated  among  the  members  of  the  Com- 
mittee. It  was  hoped  that  they  might  be  published  by  the 
Geological  Survey  as  a  Bulletin,  but  in  that  the  Committee 
was  disappointed,  though  some  of  the  results  have  been  published 
in  bulletins  and  papers  issued  by  their  authors. 


230  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

In  June,  1905,  the  U.  S.  Geological  Survey  proposed  to  coop- 
erate with  the  Joint  Committee  to  the  extent  of  placing  the 
tests  made  at  the  St.  Louis  Laboratory  at  the  service  of  the  Com- 
mittee and  allowing  the  Committee  tne  privilege  of  advising 
as  to  what  tests  of  concrete  and  reinforced  concrete  should  be 
conducted  there.  This  cooperation  was  welcomed  by  the  Com- 
mittee and  was  brought  about  by  the  fact  that  the  Secretary 
of  the  Committee,  who  was  also  the  chairman  of  the  sub-com- 
mittee on  tests,  was  in  charge  of  the  St.  Louis  Laboratory. 

During  the  five  years  in  which  the  investigations  of  struc- 
tural materials  were  in  progress  under  the  direction  of  the  U.  S. 
Geological  Survey,  a  large  amount  of  data  relating  to  concrete 
and  reinforced  concrete  was  obtained.  These  investigations 
have  included  the  survey  of  the  constituent  materials  of  concrete 
such  as  sands,  gravels  and  crushed  stone,  in  the  various  parts 
of  the  United  States,  covering  their  strength  as  mortars  or  con- 
cretes in  various  consistencies  and  proportions. 

A  number  of  series  of  tests  of  plain  and  reinforced  concrete 
beams  were  made,  covering  the  influence  of  character  of  aggre- 
gates, proportions  and  age,  percentage  of  reinforcement,  the 
effect  of  the  variation  in  span  relative  to  the  depth,  methods 
of  anchorage  of  the  reinforcement,  etc.,  upon  strength.  A  study 
was  made  of  the  effect  of  the  personal  equation  in  tests  of  beams, 
made  by  three  construction  companies  operating  in  St.  Louis  and 
by  the  employees  of  the  testing  laboratory.  Tests  covering  bond, 
shear,  compressive  strength,  and  weight  per  cubic  foot,  for  various 
classes  of  aggregates,  were  made. 

Among  other  investigations  were  tests  of  reinforced  concrete 
slabs,  12  ft.  span  supported  at  two  and  four  edges,  of  strength 
and  other  properties  of  cement  hollow  building  blocks,  of  the 
permeability  of  cement  mortars  and  concretes,  value  of  various 
waterproofing  and  dampproofing  preparations,  effect  of  alkali 
and  sea  water  on  cement  mortars  and  concretes,  the  fire-resistive 
properties  of  concrete  and  other  structural  materials,  and  these 
have  been  made  and  published,  in  part. 

The  collation  and  study  of  the  data  obtained  were  seriously 
handicapped  through  lack  of  funds  available  for  this  purpose, 
the  large  part  of  the  appropriation  being  devoted  to  work 
urgently  required  by  the  various  Government  Bureaus.  Of  the 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE      231 

annual  Government  appropriation  of  $100,000  there  was  never 
available  more  than  $15,000  per  annum  for  investigation  of  con- 
crete and  reinforced  concrete,  and  several  years  the  amount  did 
not  exceed  $5,000  a  year.  None  of  this  was  available  for  the 
publication  of  results,  and  the  allotment  from  the  funds  pro- 
vided for  all  Government  printing  was  wholly  inadequate  for  the 
purpose. 

On  June  30,  1910,  Congress  transferred  this  work  to  the 
Bureau  of  Standards  together  with  the  data  collected.  It  is 
understood  that  arrangements  have  been  made  by  which  the 
data  of  the  tests  will  be  published  as  rapidly  as  conditions  permit. 

The  Committee  has  had  the  benefit  of  the  results  of  investi- 
gations by  a  number  of  laboratories  some  of  which  were  under 
the  direct  supervision  of  its  members.  The  extent  and  varied 
character  of  the  tests,  and  their  interpretation  by  those  in  charge, 
made  them  of  especial  value  to  the  Committee. 

The  Committee  also  has  had  the  advantage  of  investigations 
made  in  foreign  laboratories. 

At  a  meeting  of  the  Joint  Committee  at  Atlantic  City,  June 
30,  1905,  it  was  decided  to  divide  among  its  members  the  work 
of  collating  and  digesting  the  results  of  all  available  tests  on  con- 
crete and  reinforced  concrete,  and  in  pursuance  of  this  resolution, 
sub-committees  were  appointed  on  the  following  subjects: 

Historical. 

Aggregates,  Proportions  and  Mixing. 

Physical  Characteristics,  Waterproofing,  etc. 

Strength  and  Elastic  Properties. 

Simple  Reinforced  Concrete  Beams. 

T-Beams,  Floor  Slabs,  etc. 

Columns  and  Piles. 

Fire-resistive  Qualities. 

Failures  of  Concrete  Structures. 

Arches. 

A  large  amount  of  work  was  done  by  these  sub-committees 
and  extensive  reports  were  submitted  by  most  of  them.  These 
reports  were  typewritten  in  manifold  and  circulated  among  the 
members  of  the  Joint  Committee,  and  were  of  great  value  to  the 
Committee  in  arriving  at  its  conclusions. 


232  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

The  Sub-Committee  on  Ways  and  Means  raised  by  sub- 
scription about  $8,000  which  was  used  for  preliminary  investi- 
gations and  expenses  incident  to  printing  its  report  and  carrying 
on  work  of  the  Committee.  The  Committee  desires  to  express 
its  appreciation  for  contributions  and  for  donations  of  materials. 

Even  with  this  support  the  field  of  activity  of  the  Committee 
has  been  limited  in  scope  and  it  has  been  unable  to  undertake 
investigations  of  its  own. 

In  1908  the  Committee  began  the  preparation  of  the  Progress 
Report  which  was  submitted  to  the  Society  in  January,  1909. 
A  preliminary  outline  was  prepared  by  the  Secretary  and  sub- 
mitted to  the  Committee  in  October.  On  October  27,  a  meet- 
ing of  the  Joint  Committee  was  held  at  New  York,  at  which  the 
report  was  discussed  paragraph  by  paragraph  and  chapters  were 
referred  to  sub-committees  and  carefully  revised  during  the 
following  three  weeks.  The  whole,  as  thus  amended  and  revised, 
was!again  submitted  in  print  to  a  full  meeting  held  in  Philadelphia, 
December  9,  10  and  11,  and  again  was  gone  over  in  great  detail. 
As  a  result  of  those  two  meetings,  a  considerable  amount  of  matter 
which  it  was  at  first  intended  to  include  was  omitted  on  account 
of  slight  disagreements  as  to  its  form,  and  lack  of  time  to  work 
it  into  satisfactory  shape,  and  to  this  fact  may  be  attributed  some 
of  the  criticisms  which  have  been  elicited.  It  is  hoped,  in  this 
report,  to  avoid  these  objections. 

In  the  spring  of  1911  the  work  of  revising  the  1909  progress 
report  was  taken  up  and  a  number  of  meetings  were  held.  The 
discussions  submitted  to  the  American  Society  of  Civil  Engineers 
and  subsequent  papers  relating  to  the  same  subject  were  care- 
fully considered,  and  differences  of  opinion  between  members  of 
the  Committee  were  threshed  out. 

Through  the  cooperation  of  the  societies  represented  on 
the  Joint  Committee  the  report  was  again  put  in  type  and  the 
necessary  editions  were  printed  for  the  use  of  the  members  of 
the  Committee,  the  last  bearing  the  date  of  August  1,  1911. 
In  the  form  thus  reached  the  report  remained  until  November 
20,  1912,  when  the  Committee  again  met  in  New  York  and  gave 
a  final  review  needed  to  bring  it  into  the  shape  in  which  it  is 
now  presented. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     233 

2.     HISTORICAL  SKETCH  OF  USE  OF  CONCRETE  AND 
REINFORCED  CONCRETE. 

In  considering  the  history  of  concrete  and  reinforced  concrete, 
a  distinction  should  be  made  between  the  two.  The  use  of  con- 
crete extends  back  to  long  before  the  Christian  era — while  on  the 
other  hand  the  art  of  reinforced  concrete  is  in  its  infancy. 

The  use  of  concrete  by  the  ancient  Romans  was  due  to  the 
discovery  of  the  fact  that  volcanic  ash  or  puzzolan,  when  mixed 
with  slaked  lime,  made  a  cement  possessing  hydraulic  properties. 
The  durability  of  this  work  of  the  Romans  was  due  largely  to 
favorable  climatic  conditions  and  the  character  of  the  cement  used. 

From  the  downfall  of  the  Roman  Empire  to  the  last  half  of 
the  eighteenth  century  the  manufacture  of  cement  seems  to  have 
been  discontinued.  The  Roman  cement  mortars  and  concretes 
surviving  the  ravages  of  the  elements  became  so  hard  that  the 
cement  acquired  a  reputation  that  led  the  early  experimenters 
of  the  eighteenth  century  to  seek  to  recover  this  supposed  lost 
Roman  art.  Evidently  no  concrete  was  used  during  this  period, 
for  the  necessity  of  simultaneous  induration  in  the  interior  and 
exterior  of  the  mass  prevents  the  use  of  lime  alone  in  concrete 
and  requires  the  use  of  some  material  having  hydraulic  qualities. 
This  fact  limited  the  use  of  concrete  to  regions  where  hydraulic 
limes  and  cements  were  to  be  found. 

In  1756  Smeaton  discovered  that  an  argillaceous  limestone 
produced  a  lime  that  would  set  and  harden  under  water,  but  no 
immediate  appreciation  of  this  knowledge  appears  to  have  resulted. 

Natural  cement  was  first  manufactured  by  Parker  in  1795 
as  a  result  of  an  attempt  to  equal  or  excel  Roman  cement,  and 
in  1796  he  took  out  an  English  patent.  Natural  cement  was 
first  produced  in  America  in  1818  and  for  a  long  time  was  the 
principal  cement  used.  With  the  introduction  of  Portland 
cement,  and  the  reduction  in  the  cost  of  manufacture,  there 
has  been  a  gradual  substitution  of  Portland  for  natural  cement. 
The  production  of  natural  cement  reached  a  maximum  of  nearly 
10,000,000  barrels  in  1899  and  has  since  gradually  decreased  to 
about  900,000  barrels  in  1911. 

The  art  of  manufacturing  Portland  cement  was  discovered 
in  1811  by  Joseph  Aspdin  and  patented  by  him  in  1824.  He 


234  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

called  this  cement  "Portland"  by  reason  of  its  resemblance  to  a 
building  stone  obtained  from  the  Isle  of  Portland,  off  the  coast 
of  England.  •  Up  to  1850  very  little  progress  was  made  in  the 
manufacture  of  this  cement  in  England.  Since  1855,  however, 
the  increase  in  the  production  in  Europe  has  been  steady,  and  its 
superiority  has  led  to  a  gradually  increasing  use  in  such  structures 
as  require  concrete  in  mass,  as  foundations,  fortifications,  sea- 
walls, docks,  locks,  etc.  While  Portland  cement  was  first  manu- 
factured in  1824  and  was  produced  in  1871  by  David  0.  Say  lor  at 
Coplay,  Pa.,  and  by  Thomas  Millen  at  South  Bend,  Ind.,  it  was 
not  until  the  early  eighties  that  it  was  manufactured  to  any  extent 
in  America.  From  that  time  on  the  production  has  rapidly 
increased,  reaching  the  enormous  total  of  nearly  80,000,000  bar- 
rels in  1911.  This  increase  in  production  has  been  largely  stimu- 
lated by  the  reduction  in  cost  of  Portland  cement  through  the 
perfection  of  the  American  methods,  the  introduction  of  rein- 
forced concrete  and  the  extensive  use  of  cement  during  the  last 
few  years. 

In  1850  Joseph  Gibbs  obtained  a  British  patent  for  casting 
solid  walls  in  wooden  molds,  and  in  1897  C.  W.  Stevens  obtained 
a  patent  for  making  artificial  cast  stone  with  concrete.  It  is 
not  clear,  however,  that  these  inventors  were  the  first  to  use 
the  material  in  a  similar  way. 

The  origin  of  the  idea  of  increasing  the  load-carrying  capacity 
of  concrete  by  reinforcing  it  with  metal  embedded  in  it  is  gen- 
erally attributed  to  Joseph  Monier,  a  French  gardener,  who  used 
a  wire  frame  or  skeleton  embedded  in  concrete  in  the  construc- 
tion of  flower  pots,  tubs  and  tanks  in  1867,  and  for  which  he 
obtained  the  first  patent  of  the  kind  in  the  same  yearj  This 
was  not  the  first  use  of  the  material,  however,  as  Lambot  con- 
structed a  boat  of  reinforced  concrete  in  1850  which  was  exhib- 
ited at  the  Paris  Exposition  in  1853.  He  took  out  an  English 
patent  in  1855. 

In  France  in  1861,  Francois  Coignet  applied  the  principles 
of  reinforced  concrete  in  the  construction  of  beams,  arches,  pipes, 
etc.,  and  with  Monier  exhibited  some  of  their  work  at  the  Paris 
Exposition  in  1867.  Coignet  also  took  out  an  English  patent  in 
1855.  In  England  in  1854,  W.  B.  Wilkinson  took  out  a  patent 
for  a  reinforced  concrete  floor.  In  America,  Ernest  L.  Ransome 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     235 

used  metal  in  combination  with  concrete  as  early  as  1874,  and 
W.  E.  Ward  erected,  in  1875,  at  Port  Chester,  New  York,  a  house 
built  entirely  of  reinforced  concrete. 

Monier,  while  not  the  first  to  apply  it,  obtained  the  first 
patents  for  reinforced  concrete,  the  German  and  American  rights 
of  which  he  disposed  of  to  G.  A.  Wayss  and  Company  in  1880. 
Wayss  and  J.  Bauschinger  shortly  after  began  the  tests  on  this 
material  which  were  published  in  1887. 

Thaddeus  Hyatt,  an  American  engineer,  employed  David 
Kirkaldy  of  London  to  make  the  experiments  on  reinforced 
concrete  which  Hyatt  published  in  1877.  The  theories  of  Hyatt 
were  applied  in  a  practical  way  to  building  construction  in  1877 
by  H.  P.  Jackson  of  San  Francisco. 

In  America,  Ransome,  between  1874  and  1884,  constantly 
increased  his  application  of  metal  reinforcement  consisting  of 
old  wire  rope  and  hoop  iron,  gradually  realizing  the  necessity 
for  using  it  with  a  greater  regard  for  its  proper  position  in  the 
mass,  and  in  1884  took  out  the  first  patent  for  a  deformed  bar. 
Prior  to  this  reinforced  concrete  was  used  but  little  in  the  United 
States.  Ransome  built  his  first  important  structure  in  1890, 
the  Leland  Stanford  Jr.  Museum  Building,  312  ft.  long,  two 
stories  high  with  basement,  the  walls  and  floors  of  which  were  of 
reinforced  concrete.  Since  1891,  when  the  first  slabs  of  rein- 
forced concrete  were  used  in  America,  the  development  has  been 
rapid. 

The  introduction  of  this  form  of  construction  proceeded 
more  slowly  in  Europe  and  between  1891  and  1894  Moeller  in 
Germany,  Wlinsch  and  Emperger  in  Hungary,  Melan  in  Austria 
and  Hennebique  in  France  were  pioneers  in  its  development. 
Hennebique  built  reinforced  concrete  slabs  as  early  as  1879  but 
did  not  patent  his  system  of  construction  until  1892. 

The  first  published  method  of  computation  was  by  Koenen 
and  Wayss  in  1886.  Subsequent  theories  have  been  advanced 
by  de  Mazas,  Neuman,  Melan,  Coignet,  de  Tedesco,  Von  Thullie, 
Ostenfeld,  Sanders,  Spitzer,  Lutken,  Ritter,  Hatt,  Talbot,  Tur- 
neaure  and  others.  As  early  as  1884  Ransome  worked  out  methods 
of  calculation  independent  of  other  investigators,  and  in  1899 
Considere  published  his  important  series  of  tests  from  which  he 
deduced  his  methods  of  calculation. 


236  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

During  the  last  ten  years  the  earlier  theories  have  been  some- 
what modified  as  experience  has  been  gained,  and  as  the  fund  of 
experimental  knowledge  has  accumulated.  The  trend  of  the 
modifications  has  been  towards  greater  harmony  in  methods  of 
calculation.  Some  of  the  earlier  assumptions  have  been  proved 
fallacious  and  generally  abandoned.  On  the  other  hand,  some  of 
the  refinements  of  calculation,  though  known  to  be  in  accordance 
with  facts,  have,  by  general  consent,  been  discarded,  as  they 
do  not  affect  the  design  materially  or  are  taken  into  account  by  a 
modification  of  the  constants.  Among  these  are  the  value  of  the 
concrete  in  the  tension  side  of  a  beam,  and  the  lack  of  a  uniform 
modulus  of  elasticity  in  compression  of  concrete  under  widely 
varying  stress.  The  earlier  theories  did  not  deal  with  the  diagonal 
tension  under  shearing  stresses.  This  has  been  found  to  be  a  most 
important  consideration  and  much  attention  has  been  paid  to  it 
in  recent  years.  In  spite  of  the  study  which  has  already  been 
given  it,  however,  there  is  still  much  to  learn  in  this  direction. 
The  action  of  various  forms  of  reinforcement  in  columns  has 
received  much  consideration,  and  there  is  still  a  wide  difference 
of  opinion  as  to  the  efficacy  of  some  forms  of  column  reinforce- 
ment. Many  experiments  have  been  made  in  this  branch  of  the 
subject,  and  practice  appears  to  be  gradually  converging  towards 
greater  uniformity. 

In  the  preparation  of  this  historical  sketch  the  Committee 
has  endeavored  to  verify  the  facts  and  has  received  the  cooperation 
of  H.  Kempton  Dyson,  Secretary  of  the  Concrete  Institute  of 
England,  Alfred  Huser,  President  Deutscher  Beton-Verein, 
C.  von  Bach,  Otto  Leube,  of  Germany,  Karl  Naehr,  of  Austria, 
Joseph  Schustler,  of  Hungary,  and  H.  I.  Hannover,  of  Denmark, 
to  whom  the  Committee  wishes  to  acknowledge  its  appreciation 
and  thanks. 

3.      AUTHORITIES   ON   WHICH   RECOMMENDATIONS   ARE    BASED. 

It  has  been  suggested  that  a  report  such  as  this  should  in- 
clude all  the  data  upon  which  conclusions  are  based.  The  im- 
practicability of  this  may  not  be  realized  by  those  who  are  not 
familiar  with  the  enormous  quantity  of  matter  involved.  There 
are,  however,  reasons  other  than  the  magnitude  of  the  task  which 
tend  to  show  that  full  publication  is  not  advisable.  One  of 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     237 

these  is  that  most  of  the  experimental  results  have  already 
appeared  in  print  and  are  now  available,  and  a  reprint  of  them 
would  be  of  no  great  advantage  to  anyone.  Where  originally 
printed  they  are  frequently  accompanied  with  comments  and 
deductions  by  their  author,  which  are  of  great  value  as  such  but 
could  scarcely  be  copied  by  the  Committee.  Another  reason 
against  publication  is  that  in  the  large  part  of  the  experimental 
work  consulted  it  has  been  found  that  certain  vitally  important 
information,  either  with  regard  to  the  materials,  the  way  in  which 
they  are  manipulated  or  as  to  the  precise  results  reached,  are 
lacking.  The  omission  of  measurements  of  deformations,  of 
course,  frequently  renders  results  of  little  value.  While  such 
tests  may  have  some  use  on  account  of  particular  facts  developed, 
a  large  part  may  be  useless,  and  consequently  unsuitable  for 
publication.  The  difficulty  of  separating  the  valuable  from  the 
valueless  would  be  almost  insurmountable. 

It  may  not  be  improper,  however,  to  append  the  following 
list  of  authors  and  references,  as  comprising  a  considerable  part 
of  the  most  important  published  material  upon  the  subject  under 
consideration: 
C.  v.  BACH. — Compressive  Tests:   Deutsche  Bauzeitung,  1905,  68 

(No.  17).     Mitteilungen  liber  Forschungsarbeiten,  Nos.  22, 

29,  39,  45-^7,  72-74. 

E.  CANDLOT. — Cements  and  Mortars:  Ciments  et  Chaux  Hydrau- 

liques,  1898,  p.  446,  447. 
HOWARD   A.    CARSON. — Plain   and  Reinforced   Concrete   Beams: 

Boston   Transit    Commission,    10th   Annual   Report,    1904, 

Appendix  G. 
A.  CONSIDERS. — Reinforced  Beams  and  Columns:  Comptes  Rendus 

de  F Academic  des  Sciences,  CXXVII,  p.  992;    CXXIX,  p. 

467;  CXXXV,  8  Sept.,  1902;  CXL,  30  June,  1905. 

F.  v.  EMPERGER. — Forschungsarbeiten  auf  dem  Gebiete  des  Eisen- 

beions.    No.  8. 

R.  FERET. — Sur  la  compadte  des  mortiers  hydrauliques;  Annales 
des  Fonts  et  Chaussees,  1892,  II.  Composition,  Various  Tests 
of  Reinforcing:  Etude  Experimentale  du  ciment  arme",  1906. 

WILLIAM  B.  FULLER  and  SANFORD  E.  THOMPSON. — Composition 
and  Density:  Transactions  American  Society  of  Civil  Engi- 
neers, Vol.  LIX,  1907,  p.  67. 


238  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

WILLIAM  K.  HATT. — Reinforced  Concrete  Beams:  Proceedings 
American  Society  for  Testing  Materials,  Vol.  II,  1902,  p.  161; 
Journal  Western  Society  of  Engineers,  June,  1904. 

JAMES  E.  HOWARD. — Watertown  Arsenal  Tests  of  Cubes  and 
Reinforced  Columns:  Tests  of  Metals,  U.  S.  A.,  1897,  1898, 
1899,  1903,  1905,  and  1906;  Proceedings  American  Society 
for  Testing  Materials,  Vol.  VI,  1906,  p.  346. 

RICHARD  L.  HUMPHREY. — St.  Louis  Laboratory  Tests  of  Aggre- 
gates, Beams,  Prisms,  Fire  Resistance:  U.  S.  Geological 
Survey,  Bulletins  324,  329,  331,  344,  370,  and  Bureau  of 
Standards,  Technologic  Paper  2. 

GEORGE  A.  KIMBALL. — Compressive  Tests  of  Cubes:  Tests  of 
Metals,  U.  S.  A.,  1899. 

GAETANO  LANZA. — Reinforced  Columns  and  Beams:  Transactions 
American  Society  of  Civil  Engineers,  Vol.  L,  1903,  p.  483; 
Proceedings  American  Society  for  Testing  Materials,  Vol 
VI,  1906,  p.  416. 

ELMER  J.  MCCAUSTLAND. — Plain  and  Reinforced  Columns: 
Engineering  News,  Vol.  LIII,  p.  614,  June  15,  1905. 

EDGAR  MARBURG. — Reinforced  Concrete  Beams  and  Piers:  Pro- 
ceedings American  Society  for  Testing  Materials,  Vol.  IV, 
1904,  p.  508;  Vol.  IX,  1909,  p.  509. 

E.  MORSCH. — Der  Eisenbetonbau. 

CHARLES  L.  NORTON. — Fireproofing,  Protection  of  Steel  by  Concrete: 

Boston  Insurance  Engineering  Experiment  Station  Reports, 

IV  and  IX. 
LOGAN    W.    PAGE. — Properties    of    Oil-mixed    Portland    Cement 

Mortar   and   Concrete:     Transactions   American   Society   of 

Civil  Engineers,  Vol.  LXXIV,  1911,  p.  255. 
GEORGE   W.   RAFTER. — Consistency   and  Proportions:    Tests   of 

Metals,  U.  S.  A.,  1898. 
M.    RUDELOFF. — Versuche    mit    Eisenbeton-Saulen,    Beton  and 

Eisen,  March  9,  1911. 

F.  SCHULE. — Resultate  der   Untersuchung  von  Armierten  Beton. 

Zurich,  1906. 

ARTHUR  N.  TALBOT. — Prisms,  Beams,  Columns:  Proceedings 
American  Society  for  Testing  Materials,  Vol.  IV,  1904,  p.  476; 
Vol.  VII,  1907,  p.  382.  University  of  Illinois  Bulletins,  Nos. 
1,  4,  8,  10,  12,  14,  20,  22,  28,  29. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     239 

ARTHUR  N.  TALBOT  and  ARTHUR  R.  LORD. — Concrete  as  Rein- 
forcement for  Structural  Steel  Columns:  University  of  Illinois 
Bulletin,  No.  56. 

SANFORD  E.  THOMPSON. — Permeability  and  Consistency:  Pro- 
ceedings American  Society  for  Testing  Materials,  Vol.  VI, 

1906,  p.  358,  and  Vol.  VIII,  1908,  p.  500. 

FREDERICK  E.  TURNEAURE. — Beams,  Columns:  Proceedings 
American  Society  for  Testing  Materials,  Vol.  IV,  1904, 
p.  498. 

U.  S.  GEOLOGICAL  SURVEY  TESTS. — Tests  of  High-Pressure  Steam 
on  Concrete  and  of  Dampproofing  and  Waterproofing  Com- 
pounds: under  direction  of  RICHARD  L.  HUMPHREY.  Pub- 
lished by  Bureau  of  Standards,  Technologic  Papers  3  and  5. 

JOHN  L.  VAN  ORNUM. — Fatigue  in  Reinforced  Beams:  Transac- 
tions American  Society  of  Civil  Engineers,  Vol.  LVIII, 

1907,  p.  294. 

MORTON   O.   WITHEY. — Beams,    Columns:    Bulletins   University 

of  Wisconsin,  Vol.  IV,  Nos.  1,  2;  Vol.  V,  Nos.  2,  5. 
IRA  H.  WOOLSON. — Effect  of  Heat:  Proceedings  American  Society 

for  Testing  Materials,  Vol.  VI,  1906,  p.  433,  and  Vol.  VII, 

1907,  p.  404. 
Recommendations   of  British   Reinforced   Concrete   Committee, 

1907,  1911. 

Regulations  of  Prussian  Government,  1904,  1907. 
Rules  of  French  Government,  1907. 
Recommendations  of  Swiss  Society  of  Engineers  and  Architects, 

1909. 
Rules  of  the  Austrian  Ministry  of  the  Interior,  1908,  1911. 

In  addition  to  the  authorities  above  quoted,  the  Committee 
desires  to  acknowledge  with  thanks  the  discussions  of  its  progress 
report  which  have  appeared  from  time  to  time  and  to  say  that  all 
the  points  brought  out  therein  have  been  carefully  weighed. 

4.       CHARACTER    OF    REPORT    PRESENTED. 

At  the  time  of  the  appointment  of  the  Committee,  in  1904, 
there  existed  a  great  diversity  of  opinion  in  America  as  to 
methods  of  design,  safe  allowable  working  stresses  and  methods 
of  proportioning,  handling,  etc.  A  great  deal  of  experimental 


240  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

work  had  been  done,  but  there  was  need  of  a  clearing  house 
through  which  results  could  be  compared  and  divergent  views 
harmonized.  During  the  interval  between  the  appointment  of 
the  Committee  and  the  preparation  of  its  first  progress  report, 
rapid  advance  was  made  in  the  art  of  concrete  construction  aided 
by  the  results  of  the  investigations  and  the  experience  acquired 
by  constructors.  This  report,  which  was  submitted  in  1909, 
attempted  to  embody  recommendations  for  safe  methods  of 
construction  and  design  in  accordance  with  the  best  practice 
of  the  day.  It  would  have  been  impossible  for  such  a  report 
to  meet  with  the  approval  of  all,  and  the  Committee  is  well 
satisfied  that  its  most  vital  recommendations  have  met  with 
quite  general  acceptance  by  the  engineers  of  the  country. 

Since  the  appearance  of  the  first  progress  report  many 
experiments  have  been  conducted  by  some  of  the  technical  insti- 
tutions and  by  private  and  corporate  interests,  and  through  these 
and  through  longer  experience  in  construction  by  its  members 
and  others,  the  Committee  is  now  able  to  make  some  perfecting 
modifications  of  its  former  report  and  to  add  some  entirely  new 
material.  The  time  therefore  seems  opportune  for  presenting 
this  second  report  bringing  the  work  up  to  date. 

The  Committee  would  point  out  that  while  the  report  deals 
with  every  kind  of  stress  to  which  concrete  is  subjected  and 
includes  all  ordinary  conditions  of  proportioning  and  handling,  it 
does  not  go  into  all  types  of  construction  or  all  the  applications 
to  which  concrete  and  reinforced  concrete  may  be  put. 

It  is  not  to  be  assumed  that  the  Committee  in  presenting 
this  report  wishes  to  imply  that  further  improvements  are  not 
possible.  A  careful  reading  will  disclose  many  points  on  which 
the  present  deductions  are  regarded  as  only  tentative,  but  it  has 
been  the  aim  of  the  Committee  to  cover  as  fully  as  possible 
recommendations  based  on  the  present  state  of  the  art. 

This  report  is  what  the  word  implies  and  nothing  more;  it 
is  not  a  " specification,"  but  may  be  used  as  a  basis  for  specifi- 
cations. 

The  use  of  concrete  and  reinforced  concrete  involves  the 
exercise  of  good  judgment  to  a  greater  degree  than  for  any  other 
building  material. 

Rules  can  not  produce  or  supersede  judgment;   on  the  con- 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     241 

trary,  judgment  should  control  the  interpretation  and  applica- 
tion of  rules. 


II.    ADAPTABILITY  OF  CONCRETE  AND  REINFORCED  CONCRETE. 

The  adaptability  of  concrete  and  reinforced  concrete  for 
engineering  structures,  or  parts  thereof,  is  now  so  well  established 
that  they  may  be  considered  the  recognized  materials  of  con- 
struction. They  have  proved  satisfactory  materials,  when 
properly  used,  for  those  purposes  for  which  their  qualities  make 
them  particularly  suitable. 

1.     USES. 

Concrete  is  a  material  of  very  low  tensile  strength  and  cap- 
able of  sustaining  but  very  small  tensile  deformations  without 
rupture ; '  its  value  as  a  structural  material  depends  chiefly  upon 
its  durability,  its  fire-resistive  qualities,  its  strength  in  compres- 
sion, its  relatively  low  cost,  and  its  adaptability  to  placing,  espe- 
cially where  space  is  cramped  or  limited.  Its  strength  increases 
generally  with  age. 

Concrete  is  well  adapted  for  structures  in  which  the  principal 
stresses  are  compressive,  such  as  foundations,  dams,  retaining 
and  other  walls,  tunnels,  piers,  abutments,  short  columns  and, 
in  many  cases,  arches.  In  the  design  of  massive  concrete,  the 
tensile  strength  of  the  material  in  resisting  principal  stresses 
must  generally  be  neglected. 

•"'By  the  use  of  metal  reinforcement  to  resist  the  principal 
tensile  stresses,  concrete  becomes  available  for  general  use  in  a 
great  variety  of  structures  and  structural  forms.'  This  combina- 
tion of  concrete  and  metal  is  particularly  advantageous  in  the 
beam,  where  both  compression  and  tension  exist;  it  is  also  advan- 
tageous in  the  column  where  the  main  stresses  are  compressive, 
but  where  cross-bending  may  exist.  In  structures  resisting 
lateral  forces  it  possesses  advantages  over  plain  concrete  in  that  it 
may  be  designed  so  as  to  utilize  more  fully  the  strength  rather 
than  the  weight  of  the  material.  Metal  reinforcement  may  also 
be  of  value  in  distributing  cracks  due  to  shrinkage  and  tempera- 
ture changes. 


242  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

2.      PRECAUTIONS. 

Failures  of  reinforced  concrete  structures  are  usually  due 
to  any  one  or  a  combination  of  the  following  causes:  defective 
design,  poor  material,  faulty  execution,  and  premature  removal 
of  forms. 

The  defects  in  a  design  may  be  many  and  various.  The 
computations  and  assumptions  on  which  they  were  based  may 
be  faulty  and  contrary  to  the  established  principles  of  statistics 
and  mechanics;  the  unit  stresses  used  may  be  excessive,  or  the 
details  of  the  design  defective. 

Articulated  concrete  structures  designed  in  imitation  of  steel 
trusses  may  be  mentioned  as  illustrating  a  questionable  use 
of  reinforced  concrete,  and  such  structures  are  not  recommended. 

Poor  material  is  sometimes  used  for  the  concrete,  as  well  as 
for  the  reinforcement.  The  use  of  poor  aggregates,  especially 
sand,  which  have  not  been  tested  is  a  common  source  of  defect. 
Inferior  concrete  is  frequently  due  also  to  lack  of  experience  on 
the  part  of  the  contractor  and  his  superintendents,  or  to  the 
absence  of  proper  supervision. 

An  unsuitable  quality  of  metal  for  reinforcement  is  some- 
times prescribed  in  specifications,  for  the  purpose  of  reducing 
the  cost.  For  steel  structures,  a  high  grade  of  material  is  specified, 
while  the  steel  used  for  reinforcing  concrete  is  sometimes  made 
of  unsuitable,  brittle  material. 

Faulty  execution,  careless  workmanship  and  too  early 
removal  of  forms  may  generally  be  attributed  to  unintelligent 
or  insufficient  supervision. 

3.      RESPONSIBILITY   AND    SUPERVISION. 

The  design  of  reinforced  concrete  structures  should  receive 
at  least  the  same  careful  consideration  as  those  of  steel,  and 
only  engineers  with  sufficient  experience  and  good  judgment  should 
be  intrusted  with  such  work. 

The  computations  should  include  all  minor  details,  which 
are  sometimes  of  the  utmost  importance.  The  design  should 
show  clearly  the  size  and  position  of  the  reinforcement  and  should 
provide  for  proper  connection  between  the  component  parts, 
so  that  they  cannot  be  displaced.  As  the  connection  between 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     243 

reinforced  concrete  members  are  frequently  a  source  of  weakness, 
the  design  should  include  a  detailed  study  of  such  connections, 
accompanied  by  computations  to  prove  their  strength. 

While  other  engineering  structures  on  the  safety  of  which 
human  lives  depend  are  generally  designed  by  engineers  employed 
by  the  owner,  and  the  contracts  let  on  the  engineer's  design  and 
specifications,  in  accordance  with  legitimate  practice,  reinforced 
concrete  structures  frequently  are  designed  by  contractors  or  by 
engineers  commercially  interested,  and  the  contract  let  for  a 
lump  sum. 

The  construction  of  buildings  in  large  cities  is  regulated  by 
ordinances  or  building  laws,  and  the  work  is  inspected  by  munici- 
pal authorities.  For  reinforced  concrete  work,  however,  the 
limited  supervision  which  municipal  inspectors  are  able  to  give 
is  not  sufficient.  Therefore,  means  for  more  adequate  supervision 
and  inspection  should  be  provided. 

The  execution  of  the  work  should  not  be  separated  from 
the  design,  as  intelligent  supervision  and  successful  execution 
can  be  expected  only  when  both  functions  are  combined.  The 
engineer  who  prepares  the  design  and  specifications  should 
have,  therefore,  the  supervision  of  the  execution  of  the  work. 

The  Committee  recommends  the  following  rules  for  structures 
of  reinforced  concrete  for  the  purpose  of  fixing  the  responsibility 
and  providing  for  adequate  supervision  during  construction: 

(a)  Before  work  is  commenced,  complete  plans  shall  be 
prepared,  accompanied  by  specifications,  stress  computations, 
and  descriptions  showing  the  general  arrangement  and  all  details. 
The  plans  shall  show  the  size,  length,  dimensions  for  points  of 
bending,  and  exact  position  of  all  reinforcement,  including  stirrups, 
ties,  hooping  and  splicing.  The  computations  shall  give  the  loads 
assumed  separately,  such  as  dead  and  live  loads,  wind  and  impact, 
if  any,  and  the  resulting  stresses. 

(6)  The  specifications  shall  state  the  qualities  of  the  materials 
to  be  used  for  making  the  concrete,  and  the  manner  in  which 
they  are  to  be  proportioned. 

(c)  The  strength  which  the  concrete  is  expected  to  attain 
after  a  definite  period  shall  be  stated  in  the  specifications. 

(d)  The  drawings  and  specifications  shall  be  signed  by  the 
engineer  and  the  contractor. 


244  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

•  (e)  Plans  and  specifications  for  all  public  structures  should 
be  approved  by  a  legally  authorized  state  or  city  official,  and 
copies  of  such  plans  and  specifications  placed  on  file  in  his  office. 

(/)  The  approval  of  plans  and  specifications  by  other  author- 
ities shall  not  relieve  the  engineer  nor  the  contractor  of  responsi- 
bility. 

(gr)  Inspection  during  construction  shall  be  made  by  com- 
petent inspectors  employed  by  and  under  the  supervision  of  the 
engineer,  and  shall  cover  the  following : 

1.  The  materials. 

2.  The  correct  construction  and  erection  of  the  forms 

and  the  supports. 

3.  The  sizes,  shapes  and  arrangement  of  the  reinforce- 

ment. 

4.  The  proportioning,  mixing  and  placing  of  the  con- 

crete. 

5.  The  strength  of  the  concrete  by  tests  of  standard  test 

pieces  made  on  the  work. 

6.  Whether  the  concrete  is  sufficiently  hardened  before 

the  forms  and  supports  are  removed. 

7.  Prevention  of  injury  to  any  part  of  the  structure  by 

and  after  the  removal  of  the  forms. 

8.  Comparison  of  dimensions  of  all  parts  of  the  finished 

structure  with  the  plans. 

(h)  Load  tests  on  portions  of  the  finished  structure  shall 
be  made  where  there  is  reasonable  suspicion  that  the  work  has 
not  been  properly  performed,  or  that,  through  influences  of  some 
kind,  the  strength  has  been  impaired.  Loading  shall  be  carried 
to  such  a  point  that  one  and  three  quarters  times  the  calculated 
working  stresses  in  critical  parts  are  reached,  and  such  loads 
shall  cause  no  injurious  permanent  deformations.  Load  tests 
shall  not  be  made  until  after  60  days  of  hardening. 

4.      DESTRUCTIVE   AGENCIES. 

(a)  Corrosion  of  Metal  Reinforcement. — Tests  and  experi- 
ence indicate  that  steel  sufficiently  embedded  in  good  concrete 
is  well  protected  against  corrosion  no  matter  whether  located  above 
or  below  water  level  It  is  recommended  that  such  protection 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     245 

•  be  not  less  than  1  in.  in  thickness.  If  the  concrete  is  porous 
so  as  to  be  readily  permeable  by  water,  as  when  the  concrete  is 
laid  with  a  very  dry  consistency,  the  metal  may  corrode  on 
account  of  the  presence  of  moisture  and  air. 

(6)  Electrolysis. — The  most  recent  experimental  data  avail- 
able on  this  subject  seem  to  show  that  while  reinforced  concrete 
structures  may,  under  certain  conditions,  be  injured  by  the  flow 
of  electric  current  in  either  direction  between  the  reinforcing 
material  and  the  concrete,  such  injury  is  generally  to  be  expected 
only  where  voltages  are  considerably  higher  than  those  which 
usually  occur  in  concrete  structures  in  practice.  If  the  iron  be 
positive,  trouble  may  manifest  itself  by  corrosion  of  the  iron 
accompanied  by  cracking  of  the  concrete,  and,  if  the  iron  be  nega- 
tive, there  may  be  a  softening  of  the  concrete  near  the  surface 
of  the  iron,  resulting  in  a  destruction  of  the  bond.  The  former, 
or  anode  effect,  decreases  much  more  rapidly  than  the  voltage, 
and  almost  if  not  quite  disappears  at  voltages  that  are  most 
likely  to  be  encountered  in  practice.  The  cathode  effect,  on  the 
other  hand,  takes  place  even  on  very  low  voltages,  and  is  therefore 
more  important  from  a  practical  standpoint  than  that  of  the  anode. 

Structures  containing  salt  or  calcium  chloride,  even  in  very 
small  quantities,  are  very  much  more  susceptible  to  the  effects  of 
electric  currents  than  normal  concrete,  both  the  anode  and  cathode 
effects  progressing  much  more  rapidly  in  the  presence  of  chlorine. 

There  is  great  weight  of  evidence  to  show  that  normal  rein- 
forced concrete  structures  free  from  salt  are  in  very  little  danger 
under  most  practical  conditions,  while  non-reinforced  concrete 
structures  are  practically  immune  from  electrolysis  troubles. 

The  results  of  experiments  now  in  progress  may  yield  more 
conclusive  information  on  the  subject. 

(c)  Sea  JVater. — The  data  available  concerning  the  effect 
of  sea  water  on  concrete  or  reinforced  concrete  are  limited  and 
inconclusive.  Sea  walls  out  of  the  range  of  frost  action  have  been 
standing  for  many  years  without  apparent  injury.  In  many 
harbors  where  the  water  is  brackish,  through  rivers  discharg- 
ing into  them,  serious  disintegration  has  taken  place.  This  has 
occurred  chiefly  between  low  and  high  tide  levels  and  is  due, 
evidently,  in  part  to  frost.  Chemical  action  also  appears  to  be 
indicated  by  the  softening  of  the  mortar.  To  effect  the  best 


246  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

resistance  to  sea  water,  the  concrete  must  be  proportioned,  mixed 
and  placed  so  as  to  prevent  the  penetration  of  sea  water  into 
the  mass  or  through  the  joints.  The  cement  should  be  of  such 
chemical  composition  as  will  best  resist  the  action  of  sea  water; 
the  aggregates  should  be  carefully  selected,  graded  and  propor- 
tioned with  the  cement  so  as  to  secure  the  maximum  possible 
density;  the  concrete  should  be  thoroughly  mixed;  the  joints 
between  old  and  new  work  should  be  made  watertight;  and  the 
concrete  should  be  kept  from  exposure  to  sea  water  until  it  is 
thoroughly  hard  and  impervious. 

(d)  Acids. — Concrete  of  first  class  quality  thoroughly  hard- 
ened is  affected  appreciably  only  by  strong  acids  which  seriously 
injure  other  materials.     A  substance  like  manure  is  injurious  to 
green  concrete,  but.  after  the  concrete  has  hardened  thoroughly 
it  resists  the  action  of  such  acid  satisfactorily. 

(e)  Oils. — When  concrete  is  properly  made  and  the  surface 
carefully  finished  and  hardened,  it  resists  the  action  of  such  mineral 
oils  as  petroleum  and  ordinary  engine  oils.     Oils  which  contain 
fatty  acids  produce  injurious  effects,  forming  compounds  with 
the  lime  which  result  in  a  disintegration  of  the  concrete  in  con- 
tact with  them. 

(/)  Alkalies. — The  action  of  alkalies  on  concrete  is  problem- 
atical. In  the  reclamation  of  arid  land  where  the  soil  is  heavily 
charged  with  alkaline  salts  it  has  been  found  that  concrete,  stone, 
brick,  iron  and  other  materials  are  injured  under  certain  condi- 
tions. It  would  seem  that  at  the  level  of  the  ground  water  in 
an  extremely  dry  atmosphere  such  structures  are  disintegrated, 
through  the  rapid  crystallization  of  the  alkaline  salts,  resulting 
from  the  alternate  wetting  and  drying  of  the  surface.  Such 
destructive  action  can  be  prevented  by  the  use  of  a  protective 
coating  and  is  minimized  by  securing  a  dense  concrete. 

III.    MATERIALS. 

A  knowledge  of  the  properties  of  the  materials  entering  into 
concrete  and  reinforced  concrete  is  the  first  essential.  The  impor- 
tance of  the  quality  of  the  materials  used  cannot  be  overesti- 
mated, and  not  only  the  cement  but  also  the  aggregates  should 
be  subject  to  such  definite  requirements  and  tests  as  will  insure 
concrete  of  the  desired  quality. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     247 

1.     CEMENT. 

There  are  available  for  construction  purposes  Portland, 
Natural  and  Puzzolan  or  Slag  cements.  Only  Portland  cement 
is  suitable  for  reinforced  concrete. 

(a)  Portland  Cement  is  the  finely  pulverized  product  result- 
ing from  the  calcination  to  incipient  fusion  of  an  intimate  mix- 
ture of  properly  proportioned  argillaceous  and  calcareous 
materials.  It  has  a  definite  chemical  composition  varying 
within  comparatively  narrow  limits. 

Portland  cement  should  be  used  in  reinforced  concrete  con- 
struction and  any  construction  that  will  be  subject  to  shocks 
or  vibrations  or  stresses  other  than  direct  compression. 

(6)  Natural  Cement  is  the  finely  pulverized  product  resulting 
from  the  calcination  of  an  argillaceous  limestone  at  a  tempera- 
ture only  sufficient  to  drive  off  the  carbonic  acid  gas.  Although 
the  limestone  must  have  a  certain  composition,  this  composition 
may  vary  within  much  wider  limits  than  in  the  case  of  Portland 
cement.  Natural  cement  does  not  develop  its  strength  as  quickly 
nor  is  it  as  uniform  in  composition  as  Portland  cement. 

Natural  cement  may  be  used  in  massive  masonry  where 
weight  rather  than  strength  is  the  essential  feature. 

Where  economy  is  the  governing  factor  a  comparison  may 
be  made  between  the  use  of  natural  cement  and  a  leaner  mixture 
of  Portland  cement  that  will  develop  the  same  strength. 

(c)  Puzzolan  or  Slag  Cement  is  the  finely  pulverized  product 
resulting   from    grinding   a   mechanical   mixture    of    granulated 
basic  blast  furnace  slag  and  hydrated  lime. 

Puzzolan  cement  is  not  nearly  as  strong,  uniform  or  reliable 
as  Portland  or  natural  cement,  is  not  used  extensively  and  never 
in  important  work;  it  should  be  used  only  for  foundation 
work  underground  where  it  is  not  exposed  to  air  or  running 
water. 

(d)  Specifications. — The   cement   should   meet   the   require- 
ments of  the  Standard  Methods  of  Testing  and  Specifications 
for  Cement  '(see  Appendix,  p.  274),  or  as  may    be   hereafter 
amended,  the  result  of  the  joint  labors  of  special  committees  of 
the  American  Society  of  Civil  Engineers,  American  Society  for 
Testing  Materials,  American  Railway  Engineering  Association, 
and  others. 


248  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

2.   AGGREGATES. 

Extreme  care  should  be  exercised  in  selecting  the  aggregates 
for  mortar  and  concrete,  and  careful  tests  made  of  the  materials  for 
the  purpose  of  determining  their  qualities  and  the  grading  necessary 
to  secure  maximum  density1  or  a  minimum  percentage  of  voids. 

(a)  Fine  Aggregate  should  consist  of  sand,  crushed  stone,  or 
gravel  screening,  graded  from  fine  to  coarse  and  passing  when 
dry  a  screen  having  J-in.  diameter  holes;   it  preferably  should  be 
of  siliceous  material,  and  should  be  clean,  coarse,  free  from  dust, 
soft  particles,  vegetable  loam  or  other  deleterious  matter  and  not 
more  than  6  per  cent  should  pass  a  sieve  having  100  meshes  per 
linear  inch.     Fine  aggregates  should  always  be  tested. 

Fine  aggregates  should  be  of  such  quality  that  mortar  com- 
posed of  one  part  Portland  cement  and  three  parts  fine  aggregate 
by  weight  when  made  into  briquettes  will  show  a  tensile  strength 
at  least  equal  to  the  strength  of  1 :  3  mortar  of  the  same  consis- 
tency made  with  the  same  cement  and  standard  Ottawa  sand.2 
If  the  aggregate  be  of  poorer  quality  the  proportion  of  cement 
should  be  increased  in  the  mortar  to  secure  the  desired  strength. 

If  the  strength  developed  by  the  aggregate  in  the  1 : 3  mortar  is 
less  than  70  per  cent  of  the  strength  of  the  Ottawa-sand  mortar, 
the  material  should  be  rejected.  To  avoid  the  removal  of  any  coat- 
ing on  the  grains,  which  may  affect  the  strength,  bank  sands  should 
not  be  dried  before  being  made  into  mortar,  but  should  contain 
natural  moisture.  The  percentage  of  moisture  may  be  determined 
upon  a  separate  sample  for  correcting  weight.  From  10  to  40  per 
cent  more  water  may  be  required  in  mixing  bank  or  artificial  sands 
than  for  standard  Ottawa  sand  to  produce  the  same  consistency. 

(b)  Coarse  Aggregate  should  consist  of  crushed  stone  or  gravel 
which  is  retained  on  a  screen  having  i-in.  diameter  holes  and 
graded  from  the  smallest  to  the  largest  particles;    it  should  be 
clean,  hard,  durable,  and  free  from  all  deleterious  matter.     Aggre- 
gates containing  dust  and  soft,  flat  or  elongated  particles,  should 
be  excluded  from  important  structures. 

1  A  convenient  coefficient  of  density  is  the  ratio  of  the  sum  of  the  volumes  of  materials 
contained  in  a  unit  volume  to  the  total  unit  volume. 

2  A  natural  sand  obtained  at  Ottawa,  Illinois,  passing  a  screen  having  20  meshes  and 
retained  on  a  screen  having  30  meshes  per  linear  inch;  prepared  and  furnished  by  the  Ottawa 
Silica  Company,  for  2  cents  per  pound  f .  o.  b.  cars,  Ottawa,  Illinois — under  the  direction  of  the, 
Special  Committee  on  Uniform  Tests  of  Cement  of  the  American  Society  of  Civil  Engineers. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     249 

The  maximum  size  of  the  coarse  aggregate  is  governed  by 
the  character  of  the  construction. 

For  reinforced  concrete  and  for  small  masses  of  unreinforced 
concrete,  the  aggregate  must  be  small  enough  to  produce  with 
the  mortar  a  homogeneous  concrete  of  viscous  consistency  which 
will  pass  readily  between  and  easily  surround  the  reinforcement 
and  fill  all  parts  of  the  forms. 

For  concrete  in  large  masses  the  size  of  the  coarse  aggregate 
may  be  increased,  as  a  large  aggregate  produces  a  stronger  con- 
crete than  a  fine  one,  although  it  should  be  noted  that  the  danger 
of  separation  from  the  mortar  becomes  greater  as  the  size  of  the 
coarse  aggregate  increases. 

Cinder  concrete  should  not  be  used  for  reinforced  concrete 
structures.  It  may  be  allowable  in  mass  for  very  light  loads  or 
for  fire  protection  purposes.  The  cinders  used  should  be  com- 
posed of  hard,  clean,  vitreous  clinker,  free  from  sulphides, 
unburned  coal  or  ashes. 

3.     WATER. 

The  water  used  in  mixing  concrete  should  be  free  from  oil, 
acid,  alkalies,  or  organic  matter. 

4.       METAL    REINFORCEMENT. 

The  Committee  recommends  as  a  suitable  material  for  rein- 
forcement, steel  filling  the  requirements  for  structural  steel  rein- 
forcement of  the  specifications  adopted  by  the  American  Railway 
Engineering  Association  (Appendix,  p.  274). 

Where  little  bending  or  shaping  is  required,  and  also  for 
reinforcement  for  shrinkage  and  temperature  stresses,  material 
filling  the  requirements  of  the  specifications  adopted  by  the 
American  Railway  Engineering  Association  for  high-carbon  steel 
(Appendix,  p.  274)  may  be  used,  adopting  the  same  unit  stresses 
as  hereinafter  recommended  for  structural  grade  material. 

For  the  reinforcement  of  slabs,  small  beams  or  minor  details, 
or  for  reinforcement  for  shrinkage  and  temperature  stresses,  wire 
drawn  from  bars  of  the  grade  of  rivet  steel  may  be  used,  with  the 
unit  stresses  hereinafter  recommended. 

The  reinforcement  should  be  free  from  excessive  rust,  scale, 


250  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

or  coatings  of  any  character  which  would  tend  to  reduce  or 
destroy  the  bond. 

IV.     PREPARING  AND  PLACING  MORTAR  AND  CONCRETE. 
1.     PROPORTIONS. 

The  materials  to  be  used  in  concrete  should  be  carefully 
selected,  of  uniform  quality,  and  proportioned  with  a  view  to 
securing  as  nearly  as  possible  a  maximum  density. 

(a)  Unit  of  Measure. — The  unit  of  measure  should  be  the 
cubic  foot.  A  bag  of  cement,  containing  94  Ib.  net,  should  be 
considered  the  equivalent  of  one  cubic  foot. 

The  measurement  of  the  fine  and  coarse  aggregates  should 
be  by  loose  volume. 

(6)  Relation  of  Fine  and  Coarse  Aggregates. — The  fine  and 
coarse  aggregates  should  be  used  in  such  relative  proportions  as 
will  insure  maximum  density.  In  unimportant  work  it  is  suffi- 
cient to  do  this  by  individual  judgment,  using  correspondingly 
higher  proportions  of  cement;  for  important  work  these  propor- 
tions should  be  carefully  determined  by  density  experiments  and 
the  sizing  of  the  fine  and  coarse  aggregates  should  be  uniformly 
maintained  or  the  proportions  changed  to  meet  the  varying  sizes. 

(c)  Relation  of  Cement  and  Aggregates  — For  reinforced  con- 
crete construction,  one  part  of  cement  to  a  total  of  six  parts  of 
fine  and  coarse  aggregates  measured  separately  should  generally 
be  used.  For  columns,  richer  mixtures  are  generally  preferable, 
and  in  massive  masonry  or  rubble  concrete  a  mixture  of  1 : 9 
or  even  1 : 12  may  be  used. 

These  proportions  should  be  determined  by  the  strength  or 
the  wearing  qualities  required  in  the  construction  at  the  critical 
period  of  its  use.  Experienced  judgment  based  on  individual 
observation  and  tests  of  similar  conditions  in  similar  localities  is  an 
excellent  guide  as  to  the  proper  proportions  for  any  particular  case. 

For  all  important  construction,  advance  tests  should  be  made 
of  concrete  of  the  materials,  proportions  and  consistency  to  be 
used  in  the  work.  These  tests  should  be  made  under  laboratory 
conditions  to  obtain  uniformity  in  mixing,  proportioning  and 
storage,  and  in  case  the  results  do  nob  conform  to  the  require- 
ments of  the  work,  aggregates  of  a  better  quality  should  be  chosen 
or  richer  proportions  used  to  obtain  the  desired  results. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     251 

2.     MIXING. 

The  ingredients  of  concrete  should  be  thoroughly  mixed  and 
the  mixing  should  continue  until  the  cement  is  uniformly  distrib- 
uted and  the  mass  is  uniform  in  color  and  homogeneous.  As 
the  maximum  density  and  greatest  strength  of  a  given  mixture 
depend  largely  on  thorough  and  complete  mixing,  it  is  essential 
that  the  work  of  mixing  should  receive  special  attention  and  care. 

Inasmuch  as  it  is  difficult  to  determine,  by  visual  inspection, 
whether  the  concrete  is  uniformly  mixed,  especially  where  lime- 
stone or  aggregates  having  the  color  of  cement  are  used,  it  is 
essential  that  the  mixing  should  occupy  a  definite  period  of  time. 
The  minimum  time  will  depend  on  whether  the  mixing  is  done 
by  machine  or  hand. 

(a)  Measuring    Ingredients. — Methods    of    measurement    of 
the  proportions  of  the  various  ingredients  should  be  used  which 
will  secure  separate  and  uniform  measurements  of  cement,  fine 
aggregate,  coarse  aggregate,  and  water  at  all  times. 

(b)  Machine  Mixing. — When  the  conditions  will  permit,  a 
machine  mixer  of  a  type  which  insures  the  uniform  proportion- 
ing of  the  materials  throughout  the  mass  should  be  used,  as  a 
more  uniform  consistency  can  be  thus  obtained.      The  mixing 
should  continue  for  a  minimum  time  of  at  least  one  minute  after 
all  the  ingredients  are  assembled  in  the  mixer. 

(c)  Hand  Mixing. — When  it  is  necessary  to  mix  by  hand,  the 
mixing  should  be  on  a  water-tight  platform  and  especial  precau- 
tions should  be  taken  to  turn  all  the  ingredients  together  at  least 
six  times  and  until  they  are  homogeneous  in  appearance  and 
color. 

(d)  Consistency. — The  materials  should  be  mixed  wet  enough 
to  produce  a  concrete  of  such  a  consistency  as  will  flow  into  the 
forms  and  about  the  metal  reinforcement  when  used,  and  which, 
at  the  same  time,  can  be  conveyed  from  the  mixer  to  the  forms 
without  separation  of  the  coarse  aggregate  from  the  mortar. 

(e)  Retempering. — Mortar  or  concrete  should  not  be  remixed 
with  water  after  it  has  partly  set. 

3.      PLACING   CONCRETE. 

(a)  Methods. — Concrete  after  the  completion  of  the  mixing 
should  be  handled  rapidly,  and  in  as  small  masses  as  is  practicable, 


252  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

from  the  place  of  mixing  to  the  place  of  final  deposit,  and  under 
no  circumstances  should  concrete  be  used  that  has  partly  set. 
A  slow-setting  cement  should  be  used  when  a  long  time  is  likely 
to  occur  between  mixing  and  placing. 

Concrete  should  be  deposited  in  such  a  manner  as  will  per- 
mit the  most  thorough  compacting,  such  as  can  be  obtained  by 
working  with  a  straight  shovel  or  slicing  tool  kept  moving  up  and 
down  until  all  the  ingredients  have  settled  in  their  proper  place 
by  gravity  and  the  surplus  water  has  been  forced  to  the  surface. 
Special  care  should  be  exercised  to  prevent  the  formation  of 
laitance,  which  hardens  very  slowly  and  forms  a  poor  surface  on 
which  to  deposit  fresh  concrete.  All  laitance  should  be  removed. 

Before  depositing  concrete,  the  reinforcement  should  be  care- 
fully placed  in  accordance  with  the  plans,  and  adequate  means 
provided  to  hold  it  in  its  proper  position  until  the  concrete  has 
been  deposited  and  compacted;  care  should  be  taken  to  see  that 
the  forms  are  substantial  and  thoroughly  wetted  (except  in  freez- 
ing weather)  or  oiled  and  that  the  space  to  be  occupied  by  the 
concrete  is  free  from  debris.  When  the  placing  of  concrete  is 
suspended,  all  necessary  grooves  for  joining  future  work  should 
be  made  before  the  concrete  has  had  time  to  set. 

When  work  is  resumed,  concrete  previously  placed  should  be 
roughened,  thoroughly  cleansed  of  foreign  material  and  laitance, 
thoroughly  wetted  and  then  slushed  with  a  mortar  consisting 
of  one  part  Portland  cement  and  not  more  than  two  parts  fine 
aggregate. 

The  faces  of  concrete  exposed  to  premature  drying  should 
be  kept  wet  for  a  period  of  at  least  seven  days. 

(b)  Freezing   Weather. — Concrete   should   not   be   mixed   or 
deposited  at  a  freezing  temperature,  unless  special  precautions 
are  taken  to  avoid  the  use  of  materials  covered  with  ice  crystals 
or  containing  frost,  and  to  provide  means  to  prevent  the  concrete 
from  freezing  after  being  placed  in  position  and  until  it  has  thor- 
oughly hardened. 

As  the  coarse  aggregate  forms  the  greater  portion  of  the 
concrete,  it  is  particularly  important  that  this  material  be  heated 
to  well  above  the  freezing  point. 

(c)  Rubble  Concrete. — Where  the  concrete  is  to  be  deposited 
in  massive  work,  its  value  may  be  improved  and  its  cost  mate- 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     253 

rially  reduced  by  the  use  of  clean  stones  thoroughly  embedded 
in  the  concrete  as  near  together  as  is  possible  and  still  entirely 
surrounded  by  concrete. 

(d)  Under  Water. — In  placing  concrete  under  water  it  is 
essential  to  maintain  still  water  at  the  place  of  deposit.  The 
use  of  tremies,  properly  designed  and  operated,  is  a  satisfactory 
method  of  placing  concrete  through  water.  The  concrete  should 
be  mixed  very  wet  (more  so  than  is  ordinarily  permissible)  so 
that  it  will  flow  readily  through  the  tremie  and  into  the  place 
with  practically  a  level  surface. 

The  coarse  aggregate  should  be  smaller  than  ordinarily  used, 
and  never  more  than  1  in.  in  diameter.  The  use  of  gravel  facili- 
tates mixing  and  assists  the  flow  of  concrete  through  the  tremie. 
The  mouth  of  the  tremie  should  be  buried  in  the  concrete  so  that 
it  is  at  all  times  entirely  sealed  and  the  surrounding  water  pre- 
vented from  forcing  itself  into  the  tremie;  the  concrete  will  then 
discharge  without  coming  in  contact  with  the  water.  The  tremie 
should  be  suspended  so  that  it  can  be  lowered  quickly  when  it  is 
necessary  either  to  choke  off  or  prevent  too  rapid  flow;  the  lateral 
flow  should  preferably  be  not  over  15  ft. 

The  flow  should  be  continuous  in  order  to  produce  a  mono- 
lithic mass  and  to  prevent  the  formation  of  laitance  in  the  interior. 

In  large  structures  it  may  be  necessary  to  divide  the  mass 
of  concrete  into  several  small  compartments  or  units,  filling  one 
at  a  time.  With  proper  care  it  is  possible  in  this  manner  to 
obtain  as  good  results  under  water  as  in  the  air. 

V.    FORMS. 

Forms  should  be  substantial  and  unyielding,  so  that  the  con- 
crete shall  conform  to  the  designed  dimensions  and  contours,  and 
should  be  tight  in  order  to  prevent  the  leakage  of  mortar. 

The  time  for  removal  of  forms  is  one  of  the  most  important 
steps  in  the  erection  of  a  structure  of  concrete  or  reinforced  con- 
crete. Care  should  be  taken  to  inspect  the  concrete  and  ascer- 
tain its  hardness  before  removing  the  forms. 

So  many  conditions  affect  the  hardening  of  concrete,  that 
the  proper  time  for  the  removal  of  the  forms  should  be  decided 
by  some  competent  and  responsible  person,  especially  where  the 
atmospheric  conditions  are  unfavorable. 


254  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

It  may  be  stated  in  a  general  way  that  forms  should  remain  in 
place  longer  for  reinforced  concrete  than  for  plain  or  massive  con- 
crete, and  that  forms  for  floors,  beams  and  similar  horizontal  struc- 
tures should  remain  in  place  much  longer  than  for  vertical  walls. 

When  the  concrete  gives  a  distinctive  ring  under  the  blow  of 
a  hammer,  it  is  generally  an  indication  that  it  has  hardened 
sufficiently  to  permit  the  removal  of  the  forms  with  safety.  If, 
however,  the  temperature  is  such  that  there  is  any  possibility 
that  the  concrete  is  frozen,  this  test  is  not  a  safe  reliance,  as 
frozen  concrete  may  appear  to  be  very  hard. 

VI.    DETAILS  OF  CONSTRUCTION. 

1.    JOINTS. 

(a)  Concrete. — For  concrete  construction  it  is  desirable  to  cast 
the  entire  structure  at  one  operation,  but  as  this  is  not  always 
possible,  especially  in  large  structures,  it  is  necessary  to  stop  the 
work  at  some  convenient  point.  This  should  be  selected  so 
that  the  resulting  joint  may  have  the  least  possible  effect  on  the 
strength  of  the  structure.  It  is  therefore  recommended  that  the 
joint  in  columns  be  made  flush  with  the  lower  side  of  the  girders; 
that  the  joints  in  girders  be  at  a  point  midway  between  supports, 
but  should  a  beam  intersect  a  girder  at  this  point,  the  joint  should 
be  offset  a  distance  equal  to  twice  the  width  of  the  beam;  that 
the  joints  in  the  members  of  a  floor  system  should  in  general  be 
made  at  or  near  the  center  of  the  span. 

Joints  in  columns  should  be  perpendicular  to  the  axis  of  the 
column,  and  in  girders,  beams,  and  floor  slabs,  perpendicular  to 
the  plane  of  their  surfaces. 

Girders  should  never  be  constructed  over  freshly  formed 
columns  without  permitting  a  period  of  at  least  two  hours  to 
elapse,  thus  providing  for  settlement  or  shrinkage  in  the  columns. 

Shrinkage  and  contraction  joints  may  be  necessary  in 
concrete  subject  to  great  fluctuations  in  temperature.  The 
frequency  of  these  joints  will  depend,  first,  on  the  range  of  tern 
perature  to  which  the  concrete  will  be  subjected,  and  second,  on 
the  quantity  and  position  of  the  reinforcement,  These  joints 
should  be  determined  and  provided  for  in  the  design.  In  massive 
work,  such  as  retaining  walls,  abutments,  etc.,  built  without  rein- 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     255 

for  cement,  contraction  joints  should  be  provided,  at  intervals  of 
from  25  to  50  ft.  and  with  reinforcement  from  50  to  80  ft. 
(the  smaller  the  height  and  thickness,  the  closer  the  spacing), 
throughout  the  length  of  the  structure.  To  provide  against  the 
structures  being  thrown  out  of  line  by  unequal  settlement,  each 
section  of  the  wall  should  be  tongued  and  grooved  into  the 
adjoining  section.  A  groove  should  be  formed  in  the  surface  of 
the  concrete  at  vertical  joints  in  walls  or  abutments. 

Shrinkage  and  contraction  joints  should  be  lubricated  by 
either  an  application  of  petroleum  residuum  oil  or  a  similar  mate- 
rial so  as  to  permit  a  free  movement  at  the  joint  when  the  con- 
crete expands  or  contracts. 

The  insertion  of  a  sheet  of  copper  or  zinc  or  even  tarred 
paper  will  be  found  advantageous  securing  expansion  and  con- 
traction at  the  joint. 

(6)  Reinforcement. — Wherever  it  is  necessary  to  splice  ten- 
sion reinforcement  the  length  of  lap  should  be  determined  on  the 
basis  of  the  safe  bond  stress,  the  stress  in  the  bar  and  the  shear- 
ing resistance  of  the  concrete  at  the  point  of  splice;  or  a  connec- 
tion should  be  made  between  the  bars  of  sufficient  strength  to 
carry  the  stress.  Splices  at  points  of  maximum  stress  should 
be  avoided.  In  columns,  bars  more  than  f  in.  in  diameter  not 
subject  to  tension  should  be  properly  squared  and  butted  in  a 
suitable  sleeve;  smaller  bars  may  be  treated  as  indicated  for  ten- 
sion reinforcement  or  the  stress  may  be  cared  for  by  embedment 
in  large  masses  of  concrete.  At  foundations,  bearing  plates 
should  be  provided  for  supporting  the  bars,  or  the  bars  may  be 
carried  into  the  footing  a  sufficient  distance  to  transmit  the  stress 
of  the  steel  to  the  concrete  by  means  of  the  bearing  and  bond 
resistance;  in  no  case  shall  the  ends  of  the  bars  be  permitted 
merely  to  rest  on  concrete. 

2.      SHRINKAGE   AND   TEMPERATURE    CHANGES. 

Shrinkage  of  concrete,  due  to  hardening  and  contraction  from 
temperature  changes,  causes  cracks,  the  size  of  which  depends  on 
the  extent  of  the  mass.  The  resulting  stresses  are  important 
in  monolithic  construction  and  should  be  considered  carefully 
by  the  designer;  they  cannot  be  counteracted  successfully,  but 
the  effects  can  be  minimized. 


256  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

Large  cracks  produced  by  quick  hardening  or  wide  ranges 
of  temperature  can  be  broken  up  to  some  extent  into  small  cracks 
by  placing  reinforcement  in  the  concrete;  in  long  continuous 
lengths  of  concrete,  it  is  better  to  provide  shrinkage  joints  at 
points  in  the  structure  where  they  will  do  little  or  no  harm. 
Reinforcement  is  of  assistance  and  permits  longer  distances 
between  shrinkage  joints  than  when  no  reinforcement  is  used. 

Small  masses  or  thin  bodies  of  concrete  should  not  be  joined 
to  larger  or  thicker  masses  without  providing  for  shrinkage  at 
such  points.  Fillets  similar  to  those  used  in  metal  castings,  but 
of  larger  dimensions,  for  gradually  reducing  from  the  thicker  to 
the  thinner  body,  are  of  advantage. 

Shrinkage  cracks  are  likely  to  occur  at  points  where  fresh 
concrete  is  joined  to  that  which  is  set,  and  hence  in  placing  the 
concrete,  construction  joints  should  be  made  on  horizontal  and 
vertical  lines,  and,  if  possible,  at  points  where  joints  would 
naturally  occur  in  dimension  stone  masonry. 

3.       FIREPROOFING. 

The  actual  fire  tests  of  concrete  and  reinforced  concrete  have 
been  limited,  but  experience,  together  with  the  results  of  tests 
thus  far  made,  indicates  that  concrete,  on  account  of  its  low  rate 
of  heat  conductivity  and  the  fact  that  it  is  incombustible,  may 
be  used  safely  for  fireproofing  purposes. 

The  dehydration  of  concrete  probably  begins  at  about  500° 
F.  and  is  completed  at  about  900°  F.,  but  experience  indicates 
that  the  volatilization  of  the  water  absorbs  heat  from  the  sur- 
rounding mass,  which,  together  with  the  resistance  of  the  air  cells, 
tends  to  increase  the  heat  resistance  of  the  concrete,  so  that  the 
process  of  dehydration  is  very  much  retarded.  The  concrete 
that  is  actually  affected  by  fire  remains  in  position  and  affords 
protection  to  the  concrete  beneath  it. 

The  thickness  of  the  protective  coating  required  depends 
on  the  probable  duration  of  a  fire  which  is  likely  to  occur  in 
the  structure  and  should  be  based  on  the  rate  of  heat  conduc- 
tivity. The  question  of  the  conductivity  of  concrete  is  one 
which  requires  further  study  and  investigation  before  a  definite 
rate  for  different  classes  of  concrete  can  be  fully  established. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     257 

However,  for  ordinary  conditions  it  is  recommended  that  the  metal 
in  girders  and  columns  be  protected  by  a  minimum  of  2  in.  of 
concrete;  that  the  metal  in  beams  be  protected  by  a  minimum 
of  1J  in.  of  concrete,  and  that  the  metal  in  floor  slabs  be  protected 
by  a  minimum  of  1  in.  of  concrete. 

It  is  recommended  that  in  monolithic  concrete  columns,  the 
concrete  to  a  depth  of  1J  in.  be  considered  as  protective  covering 
and  not  included  in  the  effective  section. 

It  is  recommended  that  the  corners  of  columns,  girders  and 
beams  be  beveled  or  rounded,  as  a  sharp  corner  is  more  seriously 
affected  by  fire  than  a  round  one. 

4.      WATERPROOFING. 

Many  expedients  have  been  used  to  render  concrete  imper- 
vious to  water  under  normal  conditions,  and  also  under  pressure 
conditions  that  exist  in  reservoirs,  dams  and  conduits  of  various 
kinds.  Experience  shows,  however,  that  where  mortar  or  con- 
crete is  proportioned  to  obtain  the  greatest  practicable  density 
and  is  mixed  to  a  rather  wet  consistency,  the  resulting  mortar  or 
concrete  is  impervious  under  moderate  pressure. 

A  concrete  of  dry  consistency  is  more  or  less  pervious  to 
water,  and  compounds  of  various  kinds  have  been  mixed  with 
the  concrete,  or  applied  as  a  wash  to  the  surface  for  the  purpose 
of  making  it  water  tight.  Many  of  these  compounds  are  of  but 
temporary  value,  and  in  time  lose  their  power  of  imparting 
impermeability  to  the  concrete. 

In  the  case  of  subways,  long  retaining  walls  and  reservoirs, 
provided  the  concrete  itself  is  impervious,  cracks  may  be  so 
reduced  by  horizontal  and  vertical  reinforcement  properly  pro- 
portioned and  located,  that  they  are  too  minute  to  permit  leak- 
age, or  are  soon  closed  by  infiltration  of  silt. 

Coal-tar  preparations  applied  either  as  a  mastic  or  as  a  coat- 
ing on  felt  or  cloth  fabric,  are  used  for  waterproofing,  and  should 
be  proof  against  injury  by  liquids  or  gases. 

For  retaining  and  similar  walls  in  direct  contact  with  the 
earth,  the  application  of  one  or  two  coatings  of  hot  coal-tar 
pitch  to  the  thoroughly  dried  surface  of  concrete  is  an  efficient 
method  of  preventing  the  penetration  of  moisture  from  the  earth. 


258  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

5.       SURFACE    FINISH. 

Concrete  is  a  material  of  an  individual  type  and  should  not 
be  used  in  imitation  of  other  structural  materials.  One  of  the 
important  problems  connected  with  its  use  is  the  character 
of  the  finish  of  exposed  surfaces.  The  finish  of  the  surface 
should  be  determined  before  the  concrete  is  placed,  and  the 
work  conducted  so  as  to  make  possible  the  finish  desired.  For 
many  forms  of  construction  the  natural  surface  of  the  concrete 
is  unobjectionable,  but  frequently  the  marks  of  the  boards  and 
the  flat  dead  surface  are  displeasing,  making  some  special  treat- 
ment desirable.  A  treatment  of  the  surface  either  by  scrubbing 
it  while  green  or  by  tooling  it  after  it  is  hard,  which  removes 
the  film  of  mortar  and  brings  the  aggregates  of  the  concrete  into 
relief,  is  frequently  used  to  remove  the  form  markings,  break  the 
monotonous  appearance  of  the  surface,  and  make  it  more  pleas- 
ing. The  plastering  of  surfaces  should  be  avoided,  for  even  if 
carefully  done,  it  is  likely  to  peel  off  under  the  action  of  frost  or 
temperature  changes. 

VII.     DESIGN. 

1.      MASSIVE   CONCRETE. 

In  the  design  of  massive  or  plain  concrete,  no  account  should 
be  taken  of  the  tensile  strength  of  the  material,  and  sections 
should  usually  be  proportioned  so  as  to  avoid  tensile  stresses 
except  in  slight  amounts  to  resist  indirect  stresses.  This  will 
generally  be  accomplished,  in  the  case  of  rectangular  shapes,  if 
the  line  of  pressure  is  kept  within  the  middle  third  of  the  sec- 
tion, but  in  very  large  structures,  such  as  high  masonry  dams,  a 
more  exact  analysis  may  be  required.  Structures  of  massive  con- 
crete are  able  to  resist  unbalanced  lateral  forces  by  reason  of 
their  weight;  hence  the  element  of  weight  rather  than  strength 
often  determines  the  design.  A  relatively  cheap  and  weak 
concrete,  therefore,  will  often  be  suitable  for  massive  concrete 
structures. 

It  is  desirable  generally  to  provide  joints  at  intervals  to 
localize  the  effect  of  contraction. 

Massive  concrete  is  suitable  for  dams,  retaining  walls,  and 
piers  and  short  columns  in  which  the  ratio  of  length  to  least 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     259 

width  is  relatively  small.  Under  ordinary  conditions  this  ratio 
should  not  exceed  six.  It  is  also  suitable  for  arches  of  moderate 
span,  where  the  conditions  as  to  foundations  are  favorable. 

2.  REINFORCED    CONCRETE. 

By  the  use  of  metal  reinforcement  to  resist  the  principal 
tensile  stresses,  concrete  becomes  available  for  general  use  in  a 
great  variety  of  structures  and  structural  forms.  This  combina- 
tion of  concrete  and  metal  is  particularly  advantageous  in  the 
beam  where  both  compression  and  tension  exist ;  it  is  also  advan- 
tageous in  the  column  where  the  main  stresses  are  compressive, 
but  where  cross-bending  may  exist.  The  theory  of  design,  there- 
fore, will  relate  mainly  to  the  analysis  of  beams  and  columns. 

3.  GENERAL   ASSUMPTIONS. 

(a)  Loads. — The  loads  or  forces  to  be  resisted  consist  of: 

1.  The  dead  load,  which  includes  the  weight  of  the  struc- 

ture and  fixed  loads  and  forces. 

2.  The  live  load  or  the  loads  and  forces  which  are  vari- 

able. The  dynamic  effect  of  the  live  load  will  often 
require  consideration.  Any  allowance  for  the  dy- 
namic effect  is  preferably  taken  into  account  by  add- 
ing the  desired  amount  to  the  live  load  or  to  the  live 
load  stresses.  The  working  stresses  hereinafter  rec- 
ommended are  intended  to  apply  to  the  equivalent 
static  stresses  thus  determined. 

In  the  case  of  high  buildings  the  live  load  on 
columns  may  be  reduced  in  accordance  with  the 
usual  practice. 

(b)  Lengths  of  Beams  and  Columns. — The  span  length  for 
beams  and  slabs  shall  be  taken  as  the  distance  from  center  to 
center  of  supports,  but  need  not  be  taken  to  exceed  the  clear 
span  plus  the  depth  of  beam  or  slab.     Brackets  shall  not  be  con- 
sidered as  reducing  the  clear  span  in  the  sense  here  intended. 

The  length  £>f  columns  shall  be  taken  as  the  maximum 
unsupported  length. 

(c)  Internal  Stresses. — As  a  basis  for  calculations  relating  to 


260  REPORT  OP  COMMITTEE  C-2  (APPENDIX). 

the  strength  of  structures,  the  following  assumptions  are  recom- 
mended : 

1.  Calculations  will  be  made  with  reference  to  working 

stresses  and  safe  loads  rather  than  with  reference  to 
ultimate  strength  and  ultimate  loads. 

2.  A  plane  section  before   bending  remains   plane   after 

bending. 

3.  The  modulus  of  elasticity  of  concrete  in  compression 

within  the  usual  limits  of  working  stresses,  is  con- 
stant. The  distribution  of  compressive  stresses  in 
beams  therefore  is  rectilinear. 

3.  In  calculating  the  moment  of  resistance  of  beams  the 
tensile  stresses  in  the  concrete  are  neglected. 

5.  Perfect  adhesion  is  assumed  between  concrete  and  rein- 

forcement. Under  compressive  stresses  the  two 
materials  are  therefore  stressed  in  proportion  to  their 
moduli  of  elasticity. 

6.  The  ratio  of  the  modulus  of  elasticity  of  steel  to  the 

modulus  of  elasticity  of  concrete  is  taken  at  15 
except  as  modified  in  Chapter  VIII,  Section  8. 

7.  Initial  stress  in  the  reinforcement  due  to  contraction  or 

expansion  in  the  concrete  is  neglected. 

It  is  recognized  that  some  of  the  assumptions  given  herein 
are  not  entirely  borne  out  by  experimental  data.  They  are  given 
in  the  interest  of  simplicity  and  uniformity,  and  variations  from 
exact  conditions  are  taken  into  account  in  the  selection  of  formulas 
and  working  stresses. 

The  deflection  of  beams  is  affected  by  the  tensile  strength 
developed  throughout  the  length  of  the  beam.  For  calculations 
of  deflections  a  value  of  8  for  the  ratio  of  the  moduli  will  give 
results  corresponding  approximately  with  the  actual  conditions. 

4.     T-BEAMS. 

In  beam  and  slab  construction,  an  effective  bond  should  be  pro- 
vided at  the  junction  of  the  beam  and  slab.  When  the  principal 
slab  reinforcement  is  parallel  to  the  beam,  transverse  reinforcement 
should  be  used  extending  over  the  beam  and  well  into  the  slab. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     261 

Where  adequate  bond  and  shearing  resistance  between  slab 
and  web  of  beam  is  provided,  the  slab  may  be  considered  as  an 
integral  part  of  the  beam,  but  its  effective  width  shall  be  deter- 
mined by  the  following  rules: 

(a)  It  shall  not  exceed   one-fourth  of  the  span   length  of 

the  beam; 
(6)  Its  overhanging  width  on  either  side  of  the  web  shall 

not  exceed  four  times  the  thickness  of  the  slab. 

In  the  design  of  T-beams  acting  as  continuous  beams,  due 
consideration  should  be  given  to  the  compressive  stresses  at  the 
support. 

Beams  in  which  the  T-form  is  used  only  for  the  purpose  of 
providing  additional  compression  area  of  concrete  should  prefer- 
ably have  a  width  of  flange  not  more  than  three  times  the  width 
of  the  stem  and  a  thickness  of  flange  not  less  than  one-third  of 
the  depth  of  the  beam.  Both  in  this  form  and  in  the  beam  and 
slab  form  the  web  stresses  and  the  limitations  in  placing  and 
spacing  the  longitudinal  reinforcement  will  piobably  be  controlling 
factors  in  design. 

5.      FLOOR   SLABS. 

Floor  slabs  should  be  designed  and  reinforced  as  continuous 
over  the  supports.  If  the  length  of  the  slab  exceeds  1.5  times  its 
width  the  entire  load  should  be  carried  by  transverse  reinforce- 
ment. Square  slabs  may  well  be  reinforced  in  both  directions.1 


1  The  exact  distribution  of  load  on  square  and  rectangular  slabs,  supported  on  four  sides 
and  reinforced  in  both  directions  cannot  readily  be  determined.  The  following  method  of 
calculation  is  recognized  to  be  faulty,  but  it  is  offered  as  a  tentative  method  which  will  give 
results  on  the  safe  side.  The  distribution  of  load  is  first  to  be  determined  by  the  formula 

I4 


in  which  r  =  proportion  of  load  carried  by  the  transverse  reinforcement,  1  =  length  and  b  = 
breadth  of  slab.  For  various  ratio  of  1/b  the  values  of  r  are  as  follows: 

1/b  r 

0.50 

.1  0.59 

.2  0.67 

.3  0.75 

.4  0.80 

.6  0.83 

Using  the  values  above  specified  each  set  of  reinforcement  is  to  be  calculated  in  the  same 
manner  as  slabs  having  supports  on  two  sides  only,  but  the  total  amount  of  reinforcement 
thus  determined  may  be  reduced  25  per  cent,  by  gradually  increasing  the  rod  spacing  from 
the  third  point  to  the  edge  of  the  slab. 


262  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

The  continuous  flat  slab  with  multiple-way  reinforcement 
is  a  type  of  construction  used  quite  extensively,  which  has  recog- 
nized advantages  for  special  conditions,  as  in  the  case  of  ware- 
houses with  large,  open  floor  space.  At  present  a  considerable 
difference  of  opinion  exists  among  engineers  as  to  the  formulas 
and  constants  which  should  be  used,  but  experience  and  tests 
are  accumulating  data  which  it  is  hoped  will  in  the  near  future 
permit  the  formulation  of  the  principles  of  design  for  this  form 
of  construction. 

The  loads  carried  to  beams  by  slabs  which  are  reinforced 
in  two  directions  will  not  be  uniformly  distributed  to  the  sup- 
porting beam  and  its  distribution  will  depend  on  the  relative 
stiffness  of  the  slab  and  the  supporting  beam.  The  distribution 
under  ordinary  conditions  of  construction  may  be  expected  to 
be  that  in  which  the  load  on  the  beam  varies  in  accordance 
with  the  ordinates  of  a  parabola  having  its  vertex  at  the  middle 
of  the  span.  For  any  given  design,  the  probable  distribution 
should  be  ascertained  and  the  moments  in  the  beam  calculated 
accordingly. 

6.      CONTINUOUS   BEAMS   AND   SLABS. 

When  the  beam  or  slab  is  continuous  over  its  supports, 
reinforcement  should  be  fully  provided  at  points  of  negative 
moment,  and  the  stresses  in  concrete  recommended  in  Chapter 
VIII,  Section  4,  should  not  be  exceeded.  In  computing  the 
positive  and  negative  moments  in  beams  and  slabs  continuous 
over  several  supports,  due  to  uniformly  distributed  loads,  the 
following  rules  are  recommended : 

(a)  That  for  floor  slabs  the  bending  moments  at  center 

wl2 
and  at  support  be  taken  at  -^  for  both  dead  and  live 

loads,  where  w  represents  the  load  per  linear  foot 
and  1  the  span  length. 

(6)  That  for  beams  the  bending  moment  at  center  and 

wl2 
at  support  for  interior  spans  be  taken  at  ^,  and 

wl2 

for  ends  spans  it  be  taken  at  -j^~  for  center  and  adjoin- 
ing support,  for  both  dead  and  live  loads. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     263 

(c)  In  the  case  of  beams  and  slabs  continuous  for  two 

spans  only,  the  bending  moment  at  the  central  sup- 

wl2 
port  should  be  taken  as  -^~  and  near  the  middle  of 

wl2 
the  span  as  ~^. 

(d)  At    the    ends    of    continuous    beams,    the    amount    of 

negative  moment  which  will  be  developed  will  depend 
on  the  condition  of  restraint  or  fixedness,  and  this 
will  depend  on  the  form  of  construction  used. 
There  will  usually  be  some  restraint  and  there  is  likely 
to  be  considerable.  Provision  should  be  made  for 
the  negative  bending  moment,  but  as  its  amount 
will  depend  on  the  form  of  construction  the  coefficient 
cannot  be  specified  here  and  must  be  left  to  the 
judgment  of  the  designer. 

For  spans  of  unusual  length,  more  exact  calculations  should 
be  made.  Special  consideration  is  also  required  in  the  case  of. 
concentrated  loads. 

Even  if  the  center  of  the  span  is  designed  for  a  greater  bending 
moment  than  is  called  for  by  (a)  or  (&),  the  negative  moment  at 
the  support  should  not  be  taken  as  less  than  the  values  there  given. 

Where  beams  are  reinforced  uit  the  compression  side,  the 
steel  may  be  assumed  to  carry  its  proportion  of  stress  in  accord- 
ance with  the  provisions  of  Chapter  VII,  Section  3,  c-6.  In 
the  case  of  cantilever  and  continuous  beams,  tensile  and  com- 
pressive  reinforcement  over  supports  must  extend  sufficiently 
beyond  the  support  and  beyond  the  point  of  infection  to  develop 
the  requisite  bond  strength. 

7.       BOND    STRENGTH    AND    SPACING    OF    REINFORCEMENT. 

Adequate  bond  strength  should  be  provided.  The  formula 
hereinafter  given  for  bond  stresses  in  beams  is  for  straight  longi- 
tudinal bars.  In  beams  in  which  a  portion  of  the  reinforcement 
is  bent  up  near  the  end,  the  bond  stress  at  places  in  both  the 
straight  bars  and  the  bent  bars  will  be  considerably  greater  than 
for  all  the  bars  straight,  and  the  stress  at  some  point  may  be 
several  times  as  much  as  that  found  by  considering  the  stress  to 
be  uniformly  distributed  along  the  bar.  In  restrained  and  canti- 


264  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

lever  beams  full  tensile  stress  exists  in  the  reinforcing  bars  at  the 
point  of  support  and  the  bars  must  be  anchored  in  the  support 
sufficiently  to  develop  this  stress, 

In  case  of  anchorage  of  bars,  an  additional  length  of  bar 
must  be  provided  beyond  that  found  on  the  assumption  of  uni- 
form bond  stress,  for  the  reason  that  before  the  bond  resistance  at 
the  end  of  the  bar  can  be  developed  the  bar  may  have  begun  to 
slip  at  another  point  and  " running"  resistance  is  less  than  the 
resistance  before  slip  begins. 

Where  high  bond  resistance  is  required,  the  deformed  bar  is 
a  suitable  means  of  supplying  the  necessary  strength.  But  it 
should  be  recognized  that  even  with  a  deformed  bar  initial  slip 
occurs  at  early  loads,  and  that  the  ultimate  loads  obtained  in 
the  usual  tests  for  bond  resistance  may  be  misleading.  Ade- 
quate bond  strength  throughout  the  length  of  a  bar  is  prefer- 
able to  end  anchorage,  but,  as  an  additional  safeguard,  such 
anchorage  may  properly  be  used  in  special  cases.  Anchorage 
furnished  by  short  bends  at  a  right  angle  is  less  effective  than 
hooks  consisting  of  turns  through  180  deg.  j 

The  lateral  spacing  of  parallel  bars  should  not  be  less  than 
three  diameters,  from  center  to  center,  nor  should  the  distance 
from  the  side  of  the  beam  to  the  center  of  the  nearest  bar  be  less 
than  two  diameters.  The  clear  spacing  between  two  layers  of 
bars  should  not  be  less  than  1  in.  The  use  of  more  than  two 
layers  is  to  be  discouraged,  unless  the  layers  are  tied  together 
by  adequate  metal  connections,  particularly  at  and  near  points 
where  bars  are  bent  up  or  bent  down. 

8.      DIAGONAL   TENSION   AND    SHEAR. 

When  a  reinforced  concrete  beam  is  subjected  to  flexural 
action,  diagonal  tensile  stresses  are  set  up.  If,  in  a  beam  not 
having  web  reinforcement,  these  stresses  exceed  the  tensile  strength 
of  the  concrete,  failure  of  the  beam  will  ensue,  j  When  web  rein- 
forcement made  up  of  stirrups  or  of  diagonal  bars  secured  to  the 
longitudinal  reinforcement,  or  of  longitudinal  reinforcing  bars  bent 
up  at  several  points  is  used,  new  conditions  prevail,  but  even  in 
this  case  at  the  beginning  of  loading  the  diagonal  tension  developed 
is  taken  principally  by  the  concrete,  the  deformations  which  are 
developed  in  the  concrete  permitting  but  little  stress  to  be  taken 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     265 

by  the  web  reinforcement.  When  the  resistance  of  the  concrete 
to  the  diagonal  tension  is  overcome  at  any  point  in  the  depth  of 
the  beam,  greater  stress  is  at  once  set  up  in  the  web  reinforcement. 

For  homogeneous  beams  the  analytical  treatment  of  diagona 
tension  is  not  very  complex — the  diagonal  tensile  stress  is  a  func- 
tion of  the  horizontal  and  vertical  shearing  stresses  and  of  the 
horizontal  tensile  stress  at  the  point  'considered,  and  as  the  inten- 
sity of  these  three  stresses  varies  from  the  neutral  axis  to  the 
remotest  fiber,  the  intensity  of  the  diagonal  tension  will  be  different 
at  different  points  in  the  section  and  will  change  with  different 
proportionate  dimensions  of  length  to  depth  of  beam.  For  the 
composite  structure  of  reinforced  concrete  beams,  an  analysis 
of  the  web  stresses,  and  particularly  of  the  diagonal  tensile  stresses, 
is  very  complex;  and  when  the  variations  due  to  a  change  from 
no  horizontal  tensile  stress  in  the  concrete  at  remotest  fiber  to 
the  presence  of  horizontal  tensile  stress  at  some  point  below  the 
neutral  axis  are  considered,  the  problem  becomes  more  complex 
and  indefinite.  Under  these  circumstances,  in  designing,  recourse 
is  had  to  the  use  of  the  calculated  vertical  shearing  stress  as  a 
means  of  comparing  or  measuring  the  diagonal  tensile  stresses 
developed,  it  being  understood  that  the  vertical  shearing  stress 
is  not  the  numerical  equivalent  of  the  diagonal  tensile  stress  and 
even  that  there  is  not  a  constant  ratio  between  them.  It  is  here 
recommended  that  the  maximum  vertical  shearing  stress  in  a 
section  be  used  as  the  means  of  comparison  of  the  resistance 
to  diagonal  tensile  stress  developed  in  the  concrete  in  beams  not 
having  web  reinforcement. 

Even  after  the  concrete  has  reached  its  limit  of  resistance 
to  diagonal  tension,  if  the  beam  has  web  reinforcement,  conditions 
of  beam  action  will  continue  to  prevail  at  least  through  the  com- 
pression area,  and  the  web  reinforcement  will  be  called  on 
to  resist  only  a  part  of  the  web  stresses.  From  experiments 
with  beams  it  is  concluded  that  it  is  safe  practice  to  use  only 
two-thirds  of  the  external  vertical  shear  in  making  calculations 
of  the  stresses  that  come  on  stirrups,  diagonal  web  pieces,  and 
bent-up  bars,  and  it  is  here  recommended  for  calculations  in 
designing  that  two-thirds  of  the  external  vertical  shear  be  taken 
as  producing  stresses  in  web  reinforcement. 

Experiments  bearing  on  the  design  of  details  of  web  rein- 


266  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

for  cement  are  not  yet  complete  enough  to  allow  more  than  gen- 
eral  and  tentative  recommendations  to  be  made.  It  is  well 
established,  however,  that  vertical  members  attached  to  or  looped 
about  horizontal  members,  inclined  members  secured  to  hori- 
zontal members  in  such  a  way  as  to  insure  against  slip,  and  the 
bending  of  a  part  of  the  longitudinal  reinforcement  at  an  angle, 
will  increase  the  strength  of  a  beam  against  failure  by  diagonal 
tension,  and  that  a  well-designed  and  well-distributed  web  rein- 
forcement may  under  the  best  conditions  increase  the  total  verti- 
cal shear  carried  to  a  value  as  much  as  three  times  that  obtained 
when  the  bars  are  all  horizontal  and  no  web  reinforcement  is 
used.  Where  vertical  stirrups  are  used  without  being  secured 
to  the  longitudinal  reinforcement,  the  force  transmitted  between 
longitudinal  bar  and  stirrup  must  not  be  greater  than  can  be 
taken  through  the  concrete,  and  care  must  be  taken  to  provide 
for  the  larger  bond  stress  developed  in  the  longitudinal  bars 
with  this  construction  than  exists  in  the  absence  of  stirrups. 
Sufficient  bond  resistance  between  the  concrete  and  the  stirrups 
or  diagonals  must  be  provided.  Where  the  longitudinal  bars 
are  bent  up,  the  points  of  bending  of  the  several  bars  should  be 
distributed  along  a  portion  of  the  length  of  the  beam  in  such  a 
way  as  to  give  efficient  web  reinforcement  over  the  portion  of 
the  length  of  the  beam  in  which  it  is  needed.  The  higher  resist- 
ance to  diagonal  tension  failures  given  by  unit  frames  having 
the  stirrups  and  bent-up  bars  securely  connected  together  both 
longitudinally  and  laterally  is  worthy  of  recognition.  It  is  neces- 
sary that  a  limit  be  placed  on  the  amount  of  shear  which  may 
be  allowed  in  a  beam;  for  when  web  reinforcement  sufficiently 
efficient  to  give  very  high  web  resistance  is  used;  at  the  higher 
stresses  the  concrete  in  the  beam  becomes  checked  and  cracked 
in  such  a  way  as  to  endanger  its  durability  as  well  as  its  strength. 

The  section  to  be  taken  as  the  critical  section  in  the  calcula- 
tion of  shearing  stresses  will  generally  be  the  one  having  the 
maximum  vertical  shear,  though  experiments  show  that  the 
section  at  which  diagonal  tension  failures  occur  is  not  just  at  a 
support  even  though  the  shear  at  the  latter  point  be  much  greater. 

The  longitudinal  spacing  of  stirrups  or  diagonal  members 
or  the  distribution  of  the  points  of  bending  of  adjacent  bent-up 
bars  should  not  exceed  three-fourths  the  depth  of  the  beam. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     267 

It  is  important  that  adequate  bond  strength  or  anchorage 
be  provided  to  develop  fully  the  assumed  strength  of  all  web 
reinforcement. 

It  should  be  noted  that  it  is  on  the  tension  side  of  a  beam 
that  diagonal  tension  develops  in  a  critical  way,  and  that  the 
proper  connection  must  always  be  made  between  stirrups  or 
other  web  reinforcement  and  the  longitudinal  tension  reinforce- 
ment, whether  the  latter  is  on  the  lower  side  of  the  beam  or  on 
its  upper  side.  Where  negative  moment  exists,  as  is  the  case 
near  the  supports  in  a  continuous  beam,  web  reinforcement  to 
be  effective  must  be  looped  over  or  wrapped  around  or  be  con- 
nected with  the  longitudinal  tension  reinforcing  bars  at  the  top 
of  the  beam  in  the  same  way  as  is  necessary  at  the  bottom  of  the 
beam  at  sections  where  the  bending  moment  is  positive  and  the 
tension  reinforcing  bars  are  at  the  bottom  of  the  beam. 

Inasmuch  as  the  smaller  the  longitudinal  deformations  in 
the  horizontal  reinforcement  are,  the  less  the  tendency  for  the 
formation  of  diagonal  cracks,  a  beam  will  be  strengthened  against 
diagonal  tension  failure  by  so  arranging  and  proportioning  the 
horizontal  reinforcement  that  the  unit  stresses  at  points  of  large 
shear  shall  be  relatively  low. 

Where  pure  shearing  stress  occurs,  or  shearing  stress  com- 
bined with  but  a  small  amount  of  tensile  stress  in  the  concrete, 
as  when  a  concentrated  load  rests  on  a  slab  or  other  forms  of 
punching  shear  are  produced,  or  in  the  case  of  compression  pieces, 
the  element  of  tension  will  not  need  consideration,  and  the 
permissible  limit  of  the  shearing  stress  will  be  higher  than  the 
allowable  limit  when  this  stress  is  used  as  a  means  of  comparing 
diagonal  tensile  stress.  The  working  values  recommended  are 
given  in  Chapter  VIII,  Working  Stresses. 

9.     COLUMNS. 

By  columns  are  meant  compression  members  of  which  the 
ratio  of  unsupported  length  to  least  width  exceeds  about  six,  and 
which  are  provided  with  reinforcement  of  one  of  the  forms  here- 
after described. 

It  is  recommended  that  the  ratio  of  unsupported  length  of 
column  to  its  least  width  be  limited  to  15. 

The  effective  area  of  the  column  shall  be  taken  as  the.  area . 


268  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

within  the  protective  covering,  as  denned  an  Chapter  VI,  Section 
3,  or  in  the  case  of  hooped  columns  or  columns  reinforced  with 
structural  shapes  it  shall  be  taken  as  the  area  within  the  hooping 
or  structural  shapes. 

Columns  may  be  reinforced  by  longitudinal  bars,  by  bands, 
hoops,  or  spirals,  together  with  longitudinal  bars,  or  by  struc- 
tural forms  which  in  themselves  are  sufficiently  rigid  to  act  as 
columns.  The  general  effect  of  closely  spaced  hooping  is  greatly 
to  increase  the  " toughness"  of  the  column  and  its  ultimate 
strength,  but  hooping  has  little  effect  on  its  behavior  within 
the  limit  of  elasticity.  It  thus  renders  the  concrete  a  safer  and 
more  reliable  material  and  should  permit  the  use  of  a  some- 
what higher  working  stress.  The  beneficial  effects  of  "toughen- 
ing" are  adequately  provided  by  a  moderate  amount  of  hooping, 
a  larger  amount  serving  mainly  to  increase  the  ultimate  strength 
and  the  possible  deformation  before  ultimate  failure. 

Composite  columns  of  structural  steel  and  concrete  in  which 
the  steel  forms  a  column  by  itself  should  be  designed  with  caution. 
To  classify  this  type  as  a  concrete  column  reinforced  with  struc- 
tural steel  is  hardly  permissible,  as  the  steel  will  generally  take 
the  greater  part  of  the  load.  When  this  type  of  column  is 
used  the  concrete  should  not  be  relied  on  to  tie  the  steel  units 
together  or  to  transmit  stresses  from  one  unit  to  another.  The 
units  should  be  adequately  tied  together  by  tie  plates  or  lat- 
tice bars,  which,  together  with  other  details,  such  as  splices,  etc., 
should  be  designed  in  conformity  with  standard  practice  for 
structural  steel.  The  concrete  may  exert  a  beneficial  effect  in 
restraining  the  steel  from  lateral  deflection  and  also  in  increas- 
ing the  carrying  capacity  of  the  column.  The  proportion  of 
load  to  be  carried  by  the  concrete  will  depend  on  the  form  of 
the  column  and  the  method  of  construction.  Generally  for  high 
percentages  of  steel  the  concrete  will  develop  relatively  low  unit- 
stresses,  and  caution  should  be  used  in  placing  dependence  on 
the  concrete. 

The  following  recommendations  are  made  for  the  relative 
working  stresses  in  the  concrete  for  the  several  types  of  columns: 

(a)  Columns    with     longitudinal    reinforcement    only,    to 
the  extent  of  not  less  than  1  per  cent  and  not  more 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     269 

than  4  per  cent  of  the  unit  stress  recommended  for 
axial  compression  in  Chapter  VIII,  Section  3. 

(b)  Columns  with  reinforcement  of  bands,  hoops  or  spi- 

rals hereinafter  specified,  stresses  20  per  cent  higher 
than  given  for  (a),  provided  the  ratio  of  unsupported 
length  of  column  to  diameter  of  the  hooped  core  is 
not  more  than  8. 

(c)  Columns   reinforced   with   not   less   than    1    per    cent 

and  not  more  than  4  per  cent  of  longitudinal  bars 
and  with  bands,  hoops  or  spirals,  as  hereinafter  speci- 
fied; stresses  45  per  cent  higher  than  given  for  (a), 
provided  the  ratio  of  unsupported  length  of  column 
to  diameter  of  the  hooped  core  is  not  more  than  8. 

The  foregoing  recommendations  are  based  on  the  follow- 
ing conditions: 

In  all  cases  longitudinal  reinforcement  is  assumed  to  carry 
its  proportion  of  stress  in  accordance  with  Section  3.  The  hoops 
or  bands  are  not  to  be  counted  on  directly  as  adding  to  the 
strength  of  the  column. 

Bars  composing  longitudinal  reinforcement  shall  be  straight 
and  shall  have  sufficient  lateral  support  to  be  securely  held  in 
place  until  the  concrete  has  set. 

Where  hooping  is  used,  the  total  amount  of  such  reinforce- 
ment shall  be  not  less  than  1  per  cent  of  the  volume  of  the  column, 
enclosed.  The  clear  spacing  of  such  hooping  shall  be  not  greater 
than  one-sixth  the  diameter  of  the  enclosed  column  and  prefer- 
ably not  greater  than  one-tenth,  and  in  no  case  more  than  2J 
in.  Hooping  is  to  be  circular  and  the  ends  of  bands  must  be 
united  in  such  a  way  as  to  develop  their  full  strength.  Adequate 
means  must  be  provided  to  hold  bands  or  hoops  in  place  so  as  to 
form  a  column,  the  core  of  which  shall  be  straight  and  well  cen- 
tered. The  strength  of  hooped  columns  depends  very  much  upon 
the  ratio  of  length  to  diameter  of  hooped  core,  and  the  strength 
due  to  hooping  decreases  rapidly  as  this  ratio  increases  beyond 
five.  The  working  stresses  recommended  are  for  hooped  columns 
with  a  length  of  not  more  than  eight  diameters  of  the  hooped  core. 

Bending  stresses  due  to  eccentric  loads  and  lateral  forces 
must  be  provided  for  by  increasing  the  section  until  the  maxi- 
mum stress  does  not  exceed  the  values  above  specified;  and 


270  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

where  tension  is  possible  in  the  longitudinal  bars  adequate  con- 
nection between  the  ends  of  the  bars  must  be  provided  to  take 
this  tension. 

10.      REINFORCING   FOR   SHRINKAGE   AND   TEMPERATURE    STRESSES. 

When  areas  of  concrete  too  large  to  expand  and  contract 
freely  as  a  whole  are  exposed  to  atmospheric  conditions,  the 
changes  of  form  due  to  shrinkage  (resulting  from  hardening) 
and  to  action  of  temperature  are  such  that  cracks  may  occur 
in  the  mass,  unless  precautions  are  taken  to  distribute  the 
stresses  so  as  to  prevent  the  cracks  altogether  or  to  render  them 
very  small.  The  distance  apart  of  the  cracks,  and  conse- 
quently their  size,  will  be  directly  proportional  to  the  diameter 
of  the  reinforcement  and  to  the  tensile  strength  of  the  concrete, 
and  inversely  proportional  to  the  percentage  of  reinforcement  and 
also  to  its  bond  resistance  per  unit  of  surface  area.  To  be  most 
effective,  therefore,  reinforcement  (in  amount  generally  not  less 
than  one-third  of  one  per  cent)  of  a  form  which  will  develop  a 
high  bond  resistance  should  be  placed  near  the  exposed  surface 
and  be  well  distributed.  The  allowable  size  and  spacing  of  cracks 
depends  on  various  considerations,  such  as  the  necessity  for 
water-tightness,  the  importance  of  appearance  of  the  surface, 
and  the  atmospheric  changes. 

VIII.    WORKING  STRESSES. 

1.      GENERAL  ASSUMPTIONS. 

The  following  working  stresses  are  recommended  for  static 
loads.  Proper  allowances  for  vibration  and  impact  are  to  be 
added  to  live  loads  where  necessary  to  produce  an  equivalent 
static  load  before  applying  the  unit  stresses  in  proportioning  parts. 

In  selecting  the  permissible  working  stress  to  be  allowed  on 
concrete,  we  should  be  guided  by  the  working  stresses  usually 
allowed  for  other  materials  of  construction,  so  that  all  structures 
of  the  same  class  but  composed  of  different  materials  may  have 
approximately  the  same  degree  of  safety. 

The  following  recommendations  as  to  allowable  stresses  are 
given  in  the  form  of  percentages  of  the  ultimate  strength  of  the 
particular  concrete  which  is  to  be  used;  this  ultimate  strength  is 


REPORT  ON  CONCKETE  AND  REINFORCED  CONCRETE.     271 

to  be  that  developed  in  cylinders  8  in.  in  diameter  and  16  in. 
long,  of  the  consistency  described  in  Chapter  IV,  Section  2  (a), 
made  and  stored  under  laboratory  conditions,  at  an  age  of  28 
days.  In  the  absence  of  definite  knowledge  in  advance  of  con- 
struction as  to  just  what  strength  may  be  expected,  the  Com- 
mittee submits  the  following  values  as  those  which  should  be 
obtained  with  materials  and  workmanship  in  accordance  with  the 
recommendations  of  this  report. 

Although  occasional  tests  may  show  higher  results  than  those 
here  given,  the  Committee  recommends  that  these  values  should 
be  the  maximum  used  in  design. 

TABLE  OF  STRENGTHS  OF  DIFFERENT  MIXTURES  OF  CONCRETE. 

(In  Pounds  per  Square  Inch.) 

Aggregate                  1:1:2      1:1|:3  1:2:4  1:2^:5  1:3:6 

Granite,  trap  rock 3300          2800  2200  1800  1400 

Gravel,  hard  limestone  and  hard 

sandstone 3000          2500  2000  1600  1300 

Soft  limestone  and  sandstone 2200          1800  1500  1200  1000 

Cinders 800            700  600  500  400 

NOTE. — For  variations  in  the  moduli  of  elasticity  see  Chapter  VIII, 
Section  8. 

2.      BEARING. 

When  compression  is  applied  to  a  surface  of  concrete  of 
at  least  twice  the  loaded  area,  a  stress  of  32.5  per  cent  of  the 
compressive  strength  may  be  allowed. 

3.      AXIAL   COMPRESSION. 

For  concentric  compression  on  a  plain  concrete  column  or 
pier,  the  length  of  which  does  not  exceed  12  diameters,  22.5  per 
cent  of  the  compressive  strength  may  be  allowed. 

For  other  forms  of  columns  the  stresses  obtained  from  the 
ratios  given  in  Chapter  VII,  Section  9,  may  govern. 

4.      COMPRESSION   IN    EXTREME    FIBER. 

The  extreme  fiber  stress  of  a  beam,  calculated  on  the  assump- 
tion of  a  constant  modulus  of  elasticity  for  concrete  under  working 
stresses  may  be  allowed  to  reach  32.5  per  cent  of  the  compressive 
strength.  Adjacent  to  the  support  of  continuous  beams  stresses 
15  per  cent  higher  may  be  used. 


272  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

5.      SHEAR   AND    DIAGONAL   TENSION. 

In  calculations  on  beams  in  which  the  maximum  shearing 
stress  in  a  section  is  used  as  the  means  of  measuring  the  resist- 
ance to  diagonal  tension  stress,  the  following  allowable  values 
for  the  maximum  vertical  shearing  stress  are  recommended : 

(a)  For  beams  with  horizontal  bars  only  and  without  web 
reinforcement  calculated  by  the  method  given  in  the  Appendix, 
Formula  (22),  2  per  cent  of  the  compressive  strength. 

(6)  For  beams  thoroughly  reinforced  with  web  reinforce- 
ment, the  value  of  the  shearing  stress  calculated  as  for  (a)  (that  is, 
using  the  total  external  vertical  shear  in  the  Formula  (22)  for 
shearing  unit  stress)  must  not  exceed  6  per  cent  of  the  compressive 
strength.  The  web  reinforcement,  exclusive  of  bent-up  bars, 
in  this  case  shall  be  proportioned  to  resist  two-thirds  of  the  external 
vertical  shear  in  the  formulas  given  in  the  Appendix,  Formula 
(24)  or  (25). 

(c)  For  beams  in  which  part  of  the  longitudinal  reinforce- 
ment is  used  in  the  form  of  bent-up  bars  distributed  over  a  portion 
of  the  beam  in  a  way  covering  the  requirements  for  this  type  of 
web  reinforcement,  the  limit  of  maximum  vertical  shearing  stress 
(the  stress  calculated  as  for  (a) ),  3  per  cent  of  the  compressive 
strength. 

(d)  Where  punching  shear  occurs,   that  is,  shearing  stress 
uncombined  with  compression  normal  to  the  shearing  surface, 
and  with  all  tension  normal  to  the  shearing  plane  provided  for  by 
reinforcement,  a  shearing  stress  of  6  per  cent  of  the  compressive 
strength  may  be  allowed. 

6.     BOND. 

The  bond  stress  between  concrete  and  plain  reinforcing 
bars  may  be  assumed  at  4  per  cent  of  the  compressive  strength, 
or  2  per  cent  in  the  case  of  drawn  wire. 

7.      REINFORCEMENT. 

The  tensile  or  compressive  stress  in  steel  should  not  exceed 
16,000  Ib.  per  sq.  in.  I 

In  structural  steel  members  the  working  stresses  adopted  by 
the  American  Railway  Engineering  Association  are  recommended. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     273 


8.      MODULUS    OF  ELASTICITY. 

The  value  of  the  modulus  of  elasticity  of  concrete  has  a  wide 
range,  depending  on  the  materials  used,  the  age,  the  range  of 
stresses  between  which  it  is  considered,  as  well  as  other  con- 
ditions. It  is  recommended  that  in  computations  for  the  posi- 
tion of  the  neutral  axis  and  for  the  resisting  moment  of  beams 
and  for  compression  of  concrete  in  columns  it  be  assumed  as : 

(a)  One-fifteenth  that  of  steel,  when  the  strength  of  the 

concrete  is  taken  as  2200  Ib.  per  sq.  in.  or  less. 
(6)  One-twelfth  that  of  steel,   when  the  strength  of  the 

concrete  is  taken  as  greater  than  2200  Ib.  per   sq.  in. 

or  less  than  2900  Ib.  per  sq.  in.,  and 
(c)   One-tenth   that   of   steel,    when   the   strength   of   the 

concrete  is  taken  as  greater  than  2900  Ib.  per  sq.  in. 

Although  not  rigorously  accurate,  these  assumptions  will  give 
safe  results.  For  the  deflection  of  beams  which  are  free  to  move 
longitudinally  at  the  supports,  in  using  formulas  for  deflection 
which  do  not  take  into  account  the  tensile  strength  developed  in  the 
concrete,  a  modulus  of  one-eighth  of  that  of  steel  is  recommended. 

Respectfully  submitted, 


RICHARD  L.  HUMPHREY, 

Secretary. 

J.  E.  GREINER, 
W.  K.  HATT, 
OLAF  HOFF, 
ROBERT  W.  LESLEY, 
A.  N.  TALBOT, 
WILLIAM  B.  FULLER, 
E.  LEE  HEIDENREICH, 
A.  L.  JOHNSON, 
GAETANO  LANZA 
EDGAR  MARBURG, 
CHARLES  M.  MILLS, 
LEON  S.  MOISSEIFF, 
HENRY  H.  QUIMBY, 


J.  R.  WORCESTER, 

Chairman. 
EMIL  SWENSSON, 

V ice-Chairman. 

W.  PURVES  TAYLOR, 
SANFORD  E.  THOMPSON, 
F.  E.  TURNEAURE, 
SAMUEL  TOBIAS  WAGNER, 
GEORGE  S.  WEBSTER, 
C.  W.  BOYNTON, 

F.  E.    SCHALL, 

G.  H.  SCRIBNER,  JR., 
F.  L.  THOMPSON, 
JOB  TUTHILL, 

R.  E.  GRIFFITHS, 
EDWARD  M.  HAGAR, 
S.  B.  NEWBERRY. 


IX.     APPENDIX. 


I.     STANDARD   SPECIFICATIONS. 


(a)  Cement.1 


(6)  Metal  Reinforcement.2 

6.  Steel  shall  be  made  by  the  open-hearth  process.     Rerolled 
material  will  not  be  accepted. 

7.  Plates   and   shapes   used   for   reinforcement   shall   be   of 
structural  steel  only.      Bars  and  wire  may  be  structural  steel 
or  high-carbon  steel. 

8.  The   chemical  and  physical  properties   shall   conform  to 
the  following  limits : 


Elements  Considered. 

Structural  Steel. 

High-Carbon  Steel. 

0  04  per  cent 

0  04  per  cent. 

Phosphorus,  maximum.  |  Aci(j 

0  06 

0.06 

Sulphur,  maximum  

0.05 

0.05 

Ultimate  tensile  strength. 

Desired 
60,000 

Desired 
88,000 

1,500,000* 

1,000,000 

Character  of  Fracture  

Ult.  tensile  strength 
Silky 

Ult.  tensile  strength 
Silky  or  finely 
granular 

Cold  Bends  without  Fracture 

180°  flatf 

180°  d=4tj 

*See  Paragraph   15.     f  See  Paragraphs   16  and   17.     %  "d=4t"  signifies  "around  a  pin 
whose  diameter  is  four  times  the  thickness  of  the  specimen." 

9.  The  yield  point  for  bars  and  wire,  as  indicated  by  the 
drop  of  the  beam,  shall  be  not  less  than  60  per  cent  of  the  ulti- 
mate tensile  strength. 

10.  If  the  ultimate  strength  varies  more  than  4000  Ib.  for 
structural  steel  or  6000  Ib.  for  high-carbon  steel,  a  retest  shall 
be  made  on  the  same  gage,  which,  to  be  acceptable,  shall  be 
within  5000  Ib.  for  structural  steel,  or  8000  Ib.  for  high-carbon 
steel,  of  the  desired  ultimate. 

11.  Chemical  determinations  of  the  percentages  of  carbon, 

1  Adopted  August  16,  1909,  by  the  American  Society  for  Testing  Materials.     See  Year- 
Book  for  1913,  pp.  254-258. 

2  Adopted  March  16,  1910,  by  the  American  Railway  Engineering  Association. 

(274) 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     275 

phosphorus,  sulphur  and  manganese  shall  be  made  by  the  manu- 
facturer from  a  test  ingot  taken  at  the  time  of  the  pouring  of 
each  melt  of  steel,  and  a  correct  copy  of  such  analysis  shall  be 
furnished  to  the  engineer  or  his  inspector.  Check  analyses  shall 
be  made  from  finished  material,  if  called  for,  in  which  case  an 
excess  of  25  per  cent  above  the  required  limit  will  be  allowed. 

12.  Plates,   Shapes   and   Bars. — Specimens   for   tensile   and 
bending  tests  for  plates  and  shapes  shall  be  made  by  cutting 
coupons  from  the  finished  product,  which  shall  have  both  faces 
rolled  and  both  edges  milled  to  the  form  shown  by  Fig.  1;   or 
with  both  edges  parallel;  or  they  may  be  turned  to  a  diameter  of 
f  in.  with  enlarged  ends. 

13.  Bars  shall  be  tested  in  their  finished  form. 


qp 

^>  ^  Parallel  section  not  jess  than  jT 
_o 


x* 


W'-kLi">i»  r>u  Etc. 


About  18^- 


FIG.  1. — TEST  PIECE  FOR  TENSION  TEST. 

14.  At  least  one  tensile  and  one  bending  test  shall  be  made 
from  each  melt  of  steel  as  rolled.     In  case  steel  differing  f-in. 
and  more  in  thickness  is  rolled  from  one  melt,  a  test  shall  be 
made  from  the  thickest  and  thinnest  material  rolled. 

15.  For  material  less  than  TV  in.  and  more  than  f  in.  in 
thickness,   the  following  modifications  will  be  allowed   in  the 
requirements  for  elongation: 

(a)  For  each  yV  in.  in  thickness  below  fV  in.  a  deduc- 
tion of  2.5  will  be  allowed  from  the  specified  percentage. 

(6)  For  each  f  in.  in  thickness  above  f  in.,  a  deduc- 
tion of  1  will  be  allowed  from  the  specified  percentage. 

16.  Bending  tests  may  be  made  by  pressure  or  by  blows. 
Shapes  and  bars  less  than  1  in.  thick  shall  bend  as  called  for 
in  Paragraph  8. 

17.  Test  specimens  1  in.  thick  and  over  shall  bend  cold 


276  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

180  deg.  around  a  pin,  the  diameter  of  which,  for  structural  steel, 
is  twice  the  thickness  of  the  specimen,  and  for  high-carbon  steel, 
is  six  times  the  thickness  of  the  specimen,  without  fracture  on 
the  outside  of  the  bend. 

18.  Finished  material   shall   be  free   from  injurious  seams, 
flaws,  cracks,  defective  edges  or  other  defects,  and  have  a  smooth, 
uniform  and  workmanlike  finish. 

19.  Every  finished  piece  of  steel  shall  have  the  melt  number 
and  the  name  of  the  manufacturer  stamped  or  rolled  upon  it, 
except  that  bar  steel  and  other  small  parts  may  be  bundled  with 
the  above  marks  on  an  attached  metal  tag. 

20.  Material  which,  subsequent  to  the  above  tests  at  the 
mills  and  its  acceptance  there,  develops  weak  spots,  brittleness, 
cracks  or  other  imperfections,  or  isjfound  to  have  injurious  defects, 
will  be  rejected  and  shall  be  replaced  by  the  manufacturer  at  his 
own  cost. 

21.  All  reinforcing  steel  shall  be  free  from  excessive  rust, 
loose  scale,   or  other  coatings  of  any  character  which  would 
reduce  or  destroy  the  bond. 


2.    SUGGESTED  FORMULAS   FOR  REINFORCED   CON- 
CRETE CONSTRUCTION. 

These  formulas  are  based  on  the  assumptions  and  principles 
given  in  the  chapter  on  design. 

(a)  Standard  Notation. 
1.  Rectangular  Beams. 

The  following  notation  is  recommended: 

f8  =  tensile  unit  stress  in  steel. 

fc  =  compressive  unit  stress  in  concrete. 

Es  =  modulus  of  elasticity  of  steel. 

Ec  =  modulus  of  elasticity  of  concrete. 

n    =| 

M  =  moment  of  resistance,  or  bending  moment  in  general. 
A    =  steel  area. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     277 

b  =  breadth  of  beam. 

d  =  depth  of  beam  to  center  of  steel. 

k  =  ratio  of  depth  of  neutral  axis  to  effective  depth  d, 

z  =  depth  of  resultant  compression  below  top. 

j  =  ratio  of  lever  arm  of  resisting  couple  to  depth  d. 

jd  =  d— z  =  arm  of  resisting  couple. 

p  =  steel  ratio  (not  percentage). 


2.  T-Beams. 

b     =  width  of  flange. 

b'    =  width  of  stem. 

t      =  thickness  of  flange. 


3.  Beams  Reinforced  for  Compression. 

A'  =  area  of  compressive  steel. 

p'  =  steel  ratio  for  compressive  steel. 

f/  =  compressive  unit  stress  in  steel. 

C  =  total  compressive  stress  in  concrete. 

C'  =  total  compressive  stress  in  steel. 

d'  =  depth  to  center  of  compressive  steel. 

z  =  depth  to  resultant  of  C  and  C'. 


4.  Shear  and  Bond. 

V    =  total  shear. 

v     =  shearing  unit  stress. 

u     =  bond  stress  per  unit  area  of  bar. 

o     =  circumference  or  perimeter  of  bar. 

So  =  sum  of  the  perimeters  of  all  bars. 


5.  Columns. 

A  =  total  net  area. 

As  =  area  of  longitudinal  steel. 

Ac  =  area  of  concrete. 

P  =  total  safe  load. 


278 


1 .  Rectangular  Beams. 


REPORT  OF  COMMITTEE  C-2  (APPENDIX). 
(b)  Formulas. 

fc 


FIG.  2. 


Position  of  neutral  axis, 


n  +  (pn)2-pn. 


Arm  of  resisting  couple, 


[For  fg  =  15000  to  16000  and  fc=600  to  650,  j  may  be  taken  at  f.j 
Fiber  stresses, 


M 


M 


_  2M         2pf. 

Steel  ratio,  for  balanced  reinforcement, 

1 


2.  T-Beams. 


u 


FIG.  3. 


(1) 
(2) 

(3) 
(4) 

(5) 


Case  I.     When  the  neutral  axis  lies  in  the  flange,  use  the 
formulas  for  rectangular  beams. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     279 

Case  II.     When  the  neutral  axis  lies  in  the  stem. 

The  following  formulas  neglect  the  compression  in  the  stem. 
Position  of  neutral  axis, 

kj      2ndA+bt* 
2nA+2bt  ' 

Position  of  resultant  compression, 

=  3kd-2t     _t_ 

2kd-t    '3-  (7) 

Arm  of  resisting  couple, 

jd  =  d-z.  (8) 

Fiber  stresses, 

M 

(9) 


Ajd' 


f  _        Mkd         _  f  8 
Tc  —  ,  .  „  ,     ,  ,x.  ,  — 


bl(kd-£t)jd       n     1- 


(10) 


(For  approximate  results  the  formulas  for  rectangular  beams 
may  be  used.) 

The  following  formulas  take  into  account  the  compression  in 
the  stem;  they  are  recommended  where  the  flange  is  small  com- 
pared with  the  stem: 

Position  of  neutral  axis, 


=    /2ndA+(b-b')t2    .  _/DA+(b-bQt  \«       pA+(b-b')t 
\  b'  r\  b'  )  b' 

Position  of  resultant  compression, 


t(2kd-t)b  +  (kd-t)2b' 

Arm  of  resisting  couple, 

jd=d-z.  (13) 

Fiber  stresses, 


f  =  _  2Mkd 

[(2kd-t)bt-H(kd-t)2b']jd- 


280  REPORT  OF  COMMITTEE  C-2  (APPENDIX). 

3.  Beams  Reinforced  for  Compression. 


Position  of  neutral  axis, 


fp')2-n(p+p'). 


Position  of  resultant  compression, 


Arm  of  resisting  couple, 


jd  =  d— z. 
6M 


M 


1-k 


fs'=nfc 


(16) 


(17) 


(18) 


(19) 


(20) 


(21) 


4.  Shear,  Bond  and  Web  Reinforcement. 

In  the  following  formulas  So  refers  only  to  the  bars  consti- 
tuting the  tension  reinforcement  at  the  section  in  question  and 
jd  is  the  lever  arm  of  the  resisting  couple  at  the  section. 


REPORT  ON  CONCRETE  AND  REINFORCED  CONCRETE.     281 

For  rectangular  beams, 

v 

(22) 

(23) 

[For  approximate  results  j  may  be  taken  at  J.] 
The   stresses   in  web   reinforcement   may  be  estimated  by 
means  of  the  following  formulas : 
Vertical  web  reinforcement, 

Vs 
P=ld"  (24) 

Web  reinforcement  inclined  at  45°  (not  bent-up  bars). 

P  =  0.7  Ip  (25) 

in  which  P  =  stress  in  single  reinforcing  member,  V  =  amount 
of 'total  shear  assumed  as  carried  by  the  reinforcement,  and  s  = 
horizontal  spacing  of  the  reinforcing  members. 

The  same  formulas  apply  to  beams  reinforced  for  compression 
as  regards  shear  and  bond  stress  for  tensile  steel. 

For  T-Beams, 

v  =  i  /.  ,  •  (261 

b  jd  {•***/ 

V 

[For  approximate  results  j  may  be  taken  at  f .] 

5.  Columns. 

Total  safe  load, 

P=fc(Ac+nAs)=fcA(l  +  (n-l)p).  (28) 

Unit  stresses, 


fs=nfc.  (30) 


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18 


NOV  9  1936 


1 "  C 


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r-S 

•-,  N.  Y. 
.  JAN.  21,  1908 


YC  fe67!4 


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